introspection: This patch fixes nullable return values fixes for the following symbols in gtk

gtk_accel_group_query
  gtk_accel_group_from_accel_closure
  gtk_accel_label_get_accel_widget
  gtk_accessible_get_widget
  gtk_actionable_get_action_name
  gtk_app_chooser_get_app_info
  gtk_app_chooser_button_get_heading
  gtk_app_chooser_dialog_get_heading
  gtk_application_get_window_by_id
  gtk_assistant_get_nth_page
  gtk_binding_set_find
  gtk_builder_get_object
  gtk_builder_lookup_callback_symbol
  gtk_builder_get_application
  gtk_button_get_image
  gtk_cell_area_get_focus_from_sibling
  gtk_cell_renderer_start_editing
  gtk_cell_view_get_model
  gtk_cell_view_get_displayed_row
  gtk_clipboard_get_owner
  gtk_container_get_focus_child
  gtk_container_get_focus_vadjustment
  gtk_container_get_focus_hadjustment
  gtk_dialog_get_widget_for_response
  gtk_drag_get_source_widget
  gtk_drag_dest_get_target_list
  gtk_drag_source_get_target_list
  gtk_entry_completion_get_model
  gtk_entry_completion_compute_prefix
  gtk_expander_get_label_widget
  gtk_file_chooser_get_filename
  gtk_file_chooser_get_current_folder
  gtk_file_chooser_get_uri
  gtk_file_chooser_get_current_folder_uri
  gtk_file_chooser_get_preview_widget
  gtk_file_chooser_get_preview_file
  gtk_file_chooser_get_preview_filename
  gtk_file_chooser_get_preview_uri
  gtk_file_chooser_get_extra_widget
  gtk_file_chooser_get_filter
  gtk_file_chooser_native_get_accept_label
  gtk_file_chooser_native_get_cancel_label
  gtk_file_filter_get_name
  gtk_font_chooser_get_font_family
  gtk_font_chooser_get_font_face
  gtk_font_chooser_get_font
  gtk_font_chooser_get_font_desc
  gtk_font_chooser_get_font_map
  gtk_frame_get_label
  gtk_gesture_get_device
  gtk_gesture_get_window
  gtk_gl_area_get_error
  gtk_header_bar_get_title
  gtk_header_bar_get_subtitle
  gtk_header_bar_get_custom_title
  gtk_icon_info_get_filename
  gtk_icon_view_get_path_at_pos
  gtk_icon_view_get_model
  gtk_image_get_pixbuf
  gtk_image_get_animation
  gtk_label_get_mnemonic_widget
  gtk_label_get_attributes
  gtk_check_version
  gtk_menu_button_get_popup
  gtk_menu_button_get_menu_model
  gtk_menu_button_get_align_widget
  gtk_menu_button_get_popover
  gtk_menu_item_get_submenu
  gtk_menu_item_get_accel_path
  gtk_native_dialog_get_title
  gtk_native_dialog_get_transient_for
  gtk_notebook_get_nth_page
  gtk_notebook_get_tab_label_text
  gtk_notebook_get_menu_label
  gtk_notebook_get_menu_label_text
  gtk_notebook_get_group_name
  gtk_notebook_get_action_widget
  gtk_offscreen_window_get_surface
  gtk_offscreen_window_get_pixbuf
  gtk_paned_get_child1
  gtk_paned_get_child2
  gtk_places_sidebar_get_location
  gtk_places_sidebar_get_nth_bookmark
  gtk_plug_get_socket_window
  gtk_popover_get_default_widget
  gtk_progress_bar_get_text
  gtk_recent_filter_get_name
  gtk_recent_manager_lookup_item
  gtk_settings_get_default
  gtk_socket_get_plug_window
  gtk_stack_sidebar_get_stack
  gtk_stack_switcher_get_stack
  gtk_style_context_get_section
  gtk_style_context_get_parent
  gtk_style_context_get_frame_clock
  gtk_test_find_widget
  gtk_text_buffer_get_mark
  gtk_text_tag_table_lookup
  gtk_text_view_get_tabs
  gtk_text_view_toggle_cursor_visible
  gtk_text_view_get_window
  gtk_toolbar_get_nth_item
  gtk_tool_button_get_label
  gtk_tool_button_get_icon_name
  gtk_tool_button_get_label_widget
  gtk_tool_button_get_icon_widget
  gtk_tool_palette_get_drop_item
  gtk_tool_palette_get_drop_group
  gtk_tree_model_filter_convert_child_path_to_path
  gtk_tree_model_filter_convert_path_to_child_path
  gtk_tree_model_sort_convert_child_path_to_path
  gtk_tree_model_sort_convert_path_to_child_path
  gtk_tree_view_get_column
  gtk_tree_view_get_bin_window
  gtk_tree_view_column_get_widget
  gtk_tree_view_column_get_tree_view
  gtk_widget_get_frame_clock
  gtk_window_group_get_current_device_grab
  GtkTextBufferSerializeFunc

gtk/gtkaccelgroup.c

@@ -818,13 +818,13 @@ _gtk_accel_group_get_accelerables (GtkAccelGroup *accel_group)
  * @accel_group: the accelerator group to query
  * @accel_key: key value of the accelerator
  * @accel_mods: modifier combination of the accelerator
- * @n_entries: (out) (allow-none): location to return the number
+ * @n_entries: (out) (optional): location to return the number
  *     of entries found, or %NULL
  *
  * Queries an accelerator group for all entries matching @accel_key
  * and @accel_mods.
  *
- * Returns: (transfer none) (array length=n_entries): an array of
+ * Returns: (nullable) (transfer none) (array length=n_entries): an array of
  *     @n_entries #GtkAccelGroupEntry elements, or %NULL. The array
  *     is owned by GTK+ and must not be freed.
  */
@@ -854,7 +854,7 @@ gtk_accel_group_query (GtkAccelGroup   *accel_group,
  * Finds the #GtkAccelGroup to which @closure is connected;
  * see gtk_accel_group_connect().
  *
- * Returns: (transfer none): the #GtkAccelGroup to which @closure
+ * Returns: (nullable) (transfer none): the #GtkAccelGroup to which @closure
  *     is connected, or %NULL
  */
 GtkAccelGroup*

gtk/gtkaccellabel.c

@@ -352,7 +352,7 @@ gtk_accel_label_finalize (GObject *object)
  * Fetches the widget monitored by this accelerator label. See
  * gtk_accel_label_set_accel_widget().
  *
- * Returns: (transfer none): the object monitored by the accelerator label, or %NULL.
+ * Returns: (nullable) (transfer none): the object monitored by the accelerator label, or %NULL.
  **/
 GtkWidget*
 gtk_accel_label_get_accel_widget (GtkAccelLabel *accel_label)

gtk/gtkaccessible.c

@@ -207,7 +207,7 @@ gtk_accessible_set_widget (GtkAccessible *accessible,
  * The returned widget does not have a reference added, so
  * you do not need to unref it.
  *
- * Returns: (transfer none): pointer to the #GtkWidget
+ * Returns: (nullable) (transfer none): pointer to the #GtkWidget
  *     corresponding to the #GtkAccessible, or %NULL.
  *
  * Since: 2.22

gtk/gtkactionable.c

@@ -86,7 +86,7 @@ gtk_actionable_default_init (GtkActionableInterface *iface)
  *
  * See gtk_actionable_set_action_name() for more information.
  *
- * Returns: the action name, or %NULL if none is set
+ * Returns: (nullable): the action name, or %NULL if none is set
  *
  * Since: 3.4
  **/
@@ -258,3 +258,4 @@ gtk_actionable_set_detailed_action_name (GtkActionable *actionable,
     gtk_actionable_set_action_target_value (actionable, NULL);
   g_strfreev (parts);
 }
+

gtk/gtkappchooser.c

@@ -109,7 +109,7 @@ gtk_app_chooser_get_content_type (GtkAppChooser *self)
  *
  * Returns the currently selected application.
  *
- * Returns: (transfer full): a #GAppInfo for the currently selected
+ * Returns: (nullable) (transfer full): a #GAppInfo for the currently selected
  *     application, or %NULL if none is selected. Free with g_object_unref()
  *
  * Since: 3.0

gtk/gtkappchooserbutton.c

@@ -973,7 +973,7 @@ gtk_app_chooser_button_set_heading (GtkAppChooserButton *self,
  *
  * Returns the text to display at the top of the dialog.
  *
- * Returns: the text to display at the top of the dialog,
+ * Returns: (nullable): the text to display at the top of the dialog,
  *     or %NULL, in which case a default text is displayed
  */
 const gchar *

gtk/gtkappchooserdialog.c

@@ -863,7 +863,7 @@ gtk_app_chooser_dialog_set_heading (GtkAppChooserDialog *self,
  *
  * Returns the text to display at the top of the dialog.
  *
- * Returns: the text to display at the top of the dialog, or %NULL, in which
+ * Returns: (nullable): the text to display at the top of the dialog, or %NULL, in which
  *     case a default text is displayed
  */
 const gchar *

gtk/gtkapplication.c

@@ -1154,7 +1154,7 @@ gtk_application_get_windows (GtkApplication *application)
  *
  * Returns the #GtkApplicationWindow with the given ID.
  *
- * Returns: (transfer none): the window with ID @id, or
+ * Returns: (nullable) (transfer none): the window with ID @id, or
  *   %NULL if there is no window with this ID
  *
  * Since: 3.6

gtk/gtkassistant.c

@@ -1684,7 +1684,7 @@ gtk_assistant_get_n_pages (GtkAssistant *assistant)
  *
  * Returns the child widget contained in page number @page_num.
  *
- * Returns: (transfer none): the child widget, or %NULL
+ * Returns: (nullable) (transfer none): the child widget, or %NULL
  *     if @page_num is out of bounds
  *
  * Since: 2.10

gtk/gtkbindings.c

@@ -751,7 +751,7 @@ gtk_binding_set_find_interned (const gchar *set_name)
  * The @set_name can either be a name used for gtk_binding_set_new()
  * or the type name of a class used in gtk_binding_set_by_class().
  *
- * Returns: (transfer none): %NULL or the specified binding set
+ * Returns: (nullable) (transfer none): %NULL or the specified binding set
  */
 GtkBindingSet*
 gtk_binding_set_find (const gchar *set_name)

gtk/gtkbuilder.c

@@ -1444,7 +1444,7 @@ gtk_builder_add_objects_from_string (GtkBuilder   *builder,
  * Gets the object named @name. Note that this function does not
  * increment the reference count of the returned object.
  *
- * Returns: (transfer none): the object named @name or %NULL if
+ * Returns: (nullable) (transfer none): the object named @name or %NULL if
  *    it could not be found in the object tree.
  *
  * Since: 2.12
@@ -2517,7 +2517,7 @@ gtk_builder_add_callback_symbols (GtkBuilder  *builder,
  * or for any case that one might be cusomizing signal connections
  * using gtk_builder_connect_signals_full()
  *
- * Returns: The callback symbol in @builder for @callback_name, or %NULL
+ * Returns: (nullable): The callback symbol in @builder for @callback_name, or %NULL
  *
  * Since: 3.10
  */
@@ -2660,7 +2660,7 @@ gtk_builder_set_application (GtkBuilder     *builder,
  * g_application_get_default(). If you want to use another application
  * for constructing proxies, use gtk_builder_set_application().
  *
- * Returns: (transfer none): the application being used by the builder,
+ * Returns: (nullable) (transfer none): the application being used by the builder,
  *     or %NULL
  *
  * Since: 3.10

gtk/gtkbutton.c

@@ -2589,7 +2589,8 @@ gtk_button_set_image (GtkButton *button,
  * This may have been explicitly set by gtk_button_set_image()
  * or constructed by gtk_button_new_from_stock().
  *
- * Returns: (transfer none): a #GtkWidget or %NULL in case there is no image
+ * Returns: (nullable) (transfer none): a #GtkWidget or %NULL in case
+ *     there is no image
  *
  * Since: 2.6
  */

gtk/gtkcalendar.h

@@ -86,8 +86,8 @@ typedef enum
  *
  * Since: 2.14
  *
- * Returns: Newly allocated string with Pango markup with details
+ * Returns: (nullable) (transfer full): Newly allocated string with Pango markup
- * for the specified day, or %NULL.
+ *     with details for the specified day or %NULL.
  */
 typedef gchar* (*GtkCalendarDetailFunc) (GtkCalendar *calendar,
                                          guint        year,

gtk/gtkcellarea.c

@@ -3187,7 +3187,7 @@ gtk_cell_area_get_focus_siblings (GtkCellArea     *area,
  * then chose to activate the focus cell for which the event
  * cell may have been a sibling.
  *
- * Returns: (transfer none): the #GtkCellRenderer for which @renderer
+ * Returns: (nullable) (transfer none): the #GtkCellRenderer for which @renderer
  *    is a sibling, or %NULL.
  *
  * Since: 3.0

gtk/gtkcellrenderer.c

@@ -893,7 +893,7 @@ gtk_cell_renderer_activate (GtkCellRenderer      *cell,
  *
  * Passes an activate event to the cell renderer for possible processing.
  *
- * Returns: (transfer none): A new #GtkCellEditable, or %NULL
+ * Returns: (nullable) (transfer none): A new #GtkCellEditable, or %NULL
  **/
 GtkCellEditable *
 gtk_cell_renderer_start_editing (GtkCellRenderer      *cell,

gtk/gtkcellview.c

@@ -1271,7 +1271,7 @@ gtk_cell_view_set_model (GtkCellView  *cell_view,
  * Returns the model for @cell_view. If no model is used %NULL is
  * returned.
  *
- * Returns: (transfer none): a #GtkTreeModel used or %NULL
+ * Returns: (nullable) (transfer none): a #GtkTreeModel used or %NULL
  *
  * Since: 2.16
  **/
@@ -1328,7 +1328,7 @@ gtk_cell_view_set_displayed_row (GtkCellView *cell_view,
  * displayed row. If no row is currently displayed, 
  * %NULL is returned.
  *
- * Returns: the currently displayed row or %NULL
+ * Returns: (nullable) (transfer full): the currently displayed row or %NULL
  *
  * Since: 2.6
  */

gtk/gtkclipboard.c

@@ -737,7 +737,7 @@ gtk_clipboard_set_with_owner (GtkClipboard          *clipboard,
  * gtk_clipboard_clear() has not subsequently called, returns the owner set
  * by gtk_clipboard_set_with_owner().
  *
- * Returns: (transfer none): the owner of the clipboard, if any;
+ * Returns: (nullable) (transfer none): the owner of the clipboard, if any;
  *     otherwise %NULL.
  **/
 GObject *

gtk/gtkcontainer.c

@@ -2465,7 +2465,7 @@ gtk_container_set_focus_child (GtkContainer *container,
  * currently focused widget. That can be obtained by calling
  * gtk_window_get_focus().
  *
- * Returns: (transfer none): The child widget which will receive the
+ * Returns: (nullable) (transfer none): The child widget which will receive the
  *          focus inside @container when the @conatiner is focussed,
  *          or %NULL if none is set.
  *
@@ -3463,8 +3463,8 @@ gtk_container_set_focus_vadjustment (GtkContainer  *container,
  * Retrieves the vertical focus adjustment for the container. See
  * gtk_container_set_focus_vadjustment().
  *
- * Returns: (transfer none): the vertical focus adjustment, or %NULL if
+ * Returns: (nullable) (transfer none): the vertical focus adjustment, or
- *   none has been set.
+ *   %NULL if none has been set.
  **/
 GtkAdjustment *
 gtk_container_get_focus_vadjustment (GtkContainer *container)
@@ -3518,7 +3518,7 @@ gtk_container_set_focus_hadjustment (GtkContainer  *container,
  * Retrieves the horizontal focus adjustment for the container. See
  * gtk_container_set_focus_hadjustment ().
  *
- * Returns: (transfer none): the horizontal focus adjustment, or %NULL if
+ * Returns: (nullable) (transfer none): the horizontal focus adjustment, or %NULL if
  *   none has been set.
  **/
 GtkAdjustment *

gtk/gtkdialog.c

@@ -1425,7 +1425,7 @@ gtk_dialog_run (GtkDialog *dialog)
  * Gets the widget button that uses the given response ID in the action area
  * of a dialog.
  *
- * Returns: (transfer none): the @widget button that uses the given
+ * Returns: (nullable) (transfer none): the @widget button that uses the given
  *     @response_id, or %NULL.
  *
  * Since: 2.20

gtk/gtkdnd.c

@@ -890,7 +890,7 @@ gtk_drag_get_data (GtkWidget      *widget,
  *
  * Determines the source widget for a drag.
  *
- * Returns: (transfer none): if the drag is occurring
+ * Returns: (nullable) (transfer none): if the drag is occurring
  *     within a single application, a pointer to the source widget.
  *     Otherwise, %NULL.
  */
@@ -1187,7 +1187,7 @@ gtk_drag_dest_unset (GtkWidget *widget)
  * Returns the list of targets this widget can accept from
  * drag-and-drop.
  * 
- * Returns: (transfer none): the #GtkTargetList, or %NULL if none
+ * Returns: (nullable) (transfer none): the #GtkTargetList, or %NULL if none
  */
 GtkTargetList*
 gtk_drag_dest_get_target_list (GtkWidget *widget)

gtk/gtkdragsource.c

@@ -214,7 +214,7 @@ gtk_drag_source_unset (GtkWidget *widget)
  * Gets the list of targets this widget can provide for
  * drag-and-drop.
  *
- * Returns: (transfer none): the #GtkTargetList, or %NULL if none
+ * Returns: (nullable) (transfer none): the #GtkTargetList, or %NULL if none
  *
  * Since: 2.4
  */

gtk/gtkentrycompletion.c

@@ -1172,7 +1172,7 @@ gtk_entry_completion_set_model (GtkEntryCompletion *completion,
  * Returns the model the #GtkEntryCompletion is using as data source.
  * Returns %NULL if the model is unset.
  *
- * Returns: (transfer none): A #GtkTreeModel, or %NULL if none
+ * Returns: (nullable) (transfer none): A #GtkTreeModel, or %NULL if none
  *     is currently being used
  *
  * Since: 2.4
@@ -1731,8 +1731,8 @@ gtk_entry_completion_cursor_on_match (GtkEntryCompletion *completion,
  * Note that a text column must have been set for this function to work,
  * see gtk_entry_completion_set_text_column() for details. 
  *
- * Returns: (transfer full): The common prefix all rows starting with @key
+ * Returns: (nullable) (transfer full): The common prefix all rows starting with
- *   or %NULL if no row matches @key.
+ *   @key or %NULL if no row matches @key.
  *
  * Since: 3.4
  **/

gtk/gtkexpander.c

@@ -1921,7 +1921,7 @@ gtk_expander_set_label_widget (GtkExpander *expander,
  * Retrieves the label widget for the frame. See
  * gtk_expander_set_label_widget().
  *
- * Returns: (transfer none): the label widget,
+ * Returns: (nullable) (transfer none): the label widget,
  *     or %NULL if there is none
  *
  * Since: 2.4

gtk/gtkfilechooser.c

@@ -673,8 +673,8 @@ gtk_file_chooser_get_create_folders (GtkFileChooser *chooser)
  * If the file chooser is in folder mode, this function returns the selected
  * folder.
  * 
- * Returns: (type filename): The currently selected filename, or %NULL
+ * Returns: (nullable) (type filename): The currently selected filename,
- *  if no file is selected, or the selected file can't
+ *  or %NULL if no file is selected, or the selected file can't
  *  be represented with a local filename. Free with g_free().
  *
  * Since: 2.4
@@ -927,8 +927,8 @@ gtk_file_chooser_set_current_folder (GtkFileChooser *chooser,
  * currently-selected folder in that mode, use gtk_file_chooser_get_uri() as the
  * usual way to get the selection.
  * 
- * Returns: (type filename): the full path of the current folder,
+ * Returns: (nullable) (type filename): the full path of the current
- * or %NULL if the current path cannot be represented as a local
+ * folder, or %NULL if the current path cannot be represented as a local
  * filename.  Free with g_free().  This function will also return
  * %NULL if the file chooser was unable to load the last folder that
  * was requested from it; for example, as would be for calling
@@ -1021,10 +1021,10 @@ gtk_file_chooser_get_current_name (GtkFileChooser *chooser)
  * If the file chooser is in folder mode, this function returns the selected
  * folder.
  * 
- * Returns: The currently selected URI, or %NULL
+ * Returns: (nullable) (transfer full): The currently selected URI, or %NULL
- *  if no file is selected. If gtk_file_chooser_set_local_only() is set to %TRUE
+ *    if no file is selected. If gtk_file_chooser_set_local_only() is set to
- * (the default) a local URI will be returned for any FUSE locations.
+ *    %TRUE (the default) a local URI will be returned for any FUSE locations.
- * Free with g_free()
+ *    Free with g_free()
  *
  * Since: 2.4
  **/
@@ -1272,10 +1272,11 @@ gtk_file_chooser_set_current_folder_uri (GtkFileChooser *chooser,
  * currently-selected folder in that mode, use gtk_file_chooser_get_uri() as the
  * usual way to get the selection.
  * 
- * Returns: the URI for the current folder.  Free with g_free().  This
+ * Returns: (nullable) (transfer full): the URI for the current folder.
- * function will also return %NULL if the file chooser was unable to load the
+ * Free with g_free().  This function will also return %NULL if the file chooser
- * last folder that was requested from it; for example, as would be for calling
+ * was unable to load the last folder that was requested from it; for example,
- * gtk_file_chooser_set_current_folder_uri() on a nonexistent folder.
+ * as would be for calling gtk_file_chooser_set_current_folder_uri() on a
+ * nonexistent folder.
  *
  * Since: 2.4
  */
@@ -1560,7 +1561,7 @@ gtk_file_chooser_set_preview_widget (GtkFileChooser *chooser,
  * Gets the current preview widget; see
  * gtk_file_chooser_set_preview_widget().
  *
- * Returns: (transfer none): the current preview widget, or %NULL
+ * Returns: (nullable) (transfer none): the current preview widget, or %NULL
  *
  * Since: 2.4
  **/
@@ -1682,7 +1683,7 @@ gtk_file_chooser_get_use_preview_label (GtkFileChooser *chooser)
  * Gets the #GFile that should be previewed in a custom preview
  * Internal function, see gtk_file_chooser_get_preview_uri().
  *
- * Returns: (transfer full): the #GFile for the file to preview,
+ * Returns: (nullable) (transfer full): the #GFile for the file to preview,
  *     or %NULL if no file is selected. Free with g_object_unref().
  *
  * Since: 2.14
@@ -1752,7 +1753,7 @@ _gtk_file_chooser_remove_shortcut_folder (GtkFileChooser  *chooser,
  * Gets the filename that should be previewed in a custom preview
  * widget. See gtk_file_chooser_set_preview_widget().
  * 
- * Returns: (type filename): the filename to preview, or %NULL if
+ * Returns: (nullable) (type filename): the filename to preview, or %NULL if
  *  no file is selected, or if the selected file cannot be represented
  *  as a local filename. Free with g_free()
  *
@@ -1783,8 +1784,8 @@ gtk_file_chooser_get_preview_filename (GtkFileChooser *chooser)
  * Gets the URI that should be previewed in a custom preview
  * widget. See gtk_file_chooser_set_preview_widget().
  * 
- * Returns: the URI for the file to preview, or %NULL if no file is
+ * Returns: (nullable) (transfer full): the URI for the file to preview,
- * selected. Free with g_free().
+ *     or %NULL if no file is selected. Free with g_free().
  *
  * Since: 2.4
  **/
@@ -1831,7 +1832,7 @@ gtk_file_chooser_set_extra_widget (GtkFileChooser *chooser,
  * Gets the current preview widget; see
  * gtk_file_chooser_set_extra_widget().
  *
- * Returns: (transfer none): the current extra widget, or %NULL
+ * Returns: (nullable) (transfer none): the current extra widget, or %NULL
  *
  * Since: 2.4
  **/
@@ -1947,7 +1948,7 @@ gtk_file_chooser_set_filter (GtkFileChooser *chooser,
  *
  * Gets the current filter; see gtk_file_chooser_set_filter().
  *
- * Returns: (transfer none): the current filter, or %NULL
+ * Returns: (nullable) (transfer none): the current filter, or %NULL
  *
  * Since: 2.4
  **/

gtk/gtkfilechoosernative.c

@@ -199,8 +199,8 @@ G_DEFINE_TYPE_WITH_CODE (GtkFileChooserNative, gtk_file_chooser_native, GTK_TYPE
  *
  * Retrieves the custom label text for the accept button.
  *
- * Returns: The custom label, or %NULL for the default. This string is
+ * Returns: (nullable): The custom label, or %NULL for the default. This string
- * owned by GTK+ and should not be modified or freed
+ * is owned by GTK+ and should not be modified or freed
  *
  * Since: 3.20
  **/
@@ -245,8 +245,8 @@ gtk_file_chooser_native_set_accept_label (GtkFileChooserNative *self,
  *
  * Retrieves the custom label text for the cancel button.
  *
- * Returns: The custom label, or %NULL for the default. This string is
+ * Returns: (nullable): The custom label, or %NULL for the default. This string
- * owned by GTK+ and should not be modified or freed
+ * is owned by GTK+ and should not be modified or freed
  *
  * Since: 3.20
  **/

gtk/gtkfilefilter.c

@@ -432,7 +432,7 @@ gtk_file_filter_set_name (GtkFileFilter *filter,
  * 
  * Gets the human-readable name for the filter. See gtk_file_filter_set_name().
  * 
- * Returns: The human-readable name of the filter,
+ * Returns: (nullable): The human-readable name of the filter,
  *   or %NULL. This value is owned by GTK+ and must not
  *   be modified or freed.
  * 

gtk/gtkfontchooser.c

@@ -135,7 +135,7 @@ gtk_font_chooser_default_init (GtkFontChooserInterface *iface)
  *
  * If the selected font is not installed, returns %NULL.
  *
- * Returns: (transfer none): A #PangoFontFamily representing the
+ * Returns: (nullable) (transfer none): A #PangoFontFamily representing the
  *     selected font family, or %NULL. The returned object is owned by @fontchooser
  *     and must not be modified or freed.
  *
@@ -158,7 +158,7 @@ gtk_font_chooser_get_font_family (GtkFontChooser *fontchooser)
  *
  * If the selected font is not installed, returns %NULL.
  *
- * Returns: (transfer none): A #PangoFontFace representing the
+ * Returns: (nullable) (transfer none): A #PangoFontFace representing the
  *     selected font group details, or %NULL. The returned object is owned by
  *     @fontchooser and must not be modified or freed.
  *
@@ -206,7 +206,7 @@ gtk_font_chooser_get_font_size (GtkFontChooser *fontchooser)
  * Use pango_font_description_equal() if you want to compare two
  * font descriptions.
  *
- * Returns: (transfer full) (allow-none): A string with the name
+ * Returns: (nullable) (transfer full): A string with the name
  *     of the current font, or %NULL if  no font is selected. You must
  *     free this string with g_free().
  *
@@ -259,7 +259,7 @@ gtk_font_chooser_set_font (GtkFontChooser *fontchooser,
  * Use pango_font_description_equal() if you want to compare two
  * font descriptions.
  *
- * Returns: (transfer full) (allow-none): A #PangoFontDescription for the
+ * Returns: (nullable) (transfer full): A #PangoFontDescription for the
  *     current font, or %NULL if  no font is selected.
  *
  * Since: 3.2
@@ -465,7 +465,7 @@ gtk_font_chooser_set_font_map (GtkFontChooser *fontchooser,
  * Gets the custom font map of this font chooser widget,
  * or %NULL if it does not have one.
  *
- * Returns: (transfer full) (allow-none): a #PangoFontMap, or %NULL
+ * Returns: (nullable) (transfer full): a #PangoFontMap, or %NULL
  *
  * Since: 3.18
  */

gtk/gtkframe.c

@@ -487,7 +487,7 @@ gtk_frame_set_label (GtkFrame *frame,
  * for the label widget if a non-%NULL argument was passed
  * to gtk_frame_new().)
  * 
- * Returns: the text in the label, or %NULL if there
+ * Returns: (nullable): the text in the label, or %NULL if there
  *               was no label widget or the lable widget was not
  *               a #GtkLabel. This string is owned by GTK+ and
  *               must not be modified or freed.

gtk/gtkgesture.c

@@ -1015,7 +1015,7 @@ gtk_gesture_init (GtkGesture *gesture)
  * Returns the master #GdkDevice that is currently operating
  * on @gesture, or %NULL if the gesture is not being interacted.
  *
- * Returns: (transfer none) (allow-none): a #GdkDevice, or %NULL
+ * Returns: (nullable) (transfer none): a #GdkDevice, or %NULL
  *
  * Since: 3.14
  **/
@@ -1568,7 +1568,7 @@ _gtk_gesture_cancel_sequence (GtkGesture       *gesture,
  * handled by @gesture. See gtk_gesture_set_window() for more
  * information.
  *
- * Returns: (transfer none) (allow-none): the user defined window, or %NULL if none
+ * Returns: (nullable) (transfer none): the user defined window, or %NULL if none
  *
  * Since: 3.14
  **/

gtk/gtkglarea.c

@@ -998,7 +998,7 @@ gtk_gl_area_set_error (GtkGLArea    *area,
  *
  * Gets the current error set on the @area.
  *
- * Returns: (transfer none): the #GError or %NULL
+ * Returns: (nullable) (transfer none): the #GError or %NULL
  *
  * Since: 3.16
  */

gtk/gtkheaderbar.c

@@ -1220,7 +1220,7 @@ gtk_header_bar_set_title (GtkHeaderBar *bar,
  *
  * Retrieves the title of the header. See gtk_header_bar_set_title().
  *
- * Returns: the title of the header, or %NULL if none has
+ * Returns: (nullable): the title of the header, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -1281,7 +1281,7 @@ gtk_header_bar_set_subtitle (GtkHeaderBar *bar,
  *
  * Retrieves the subtitle of the header. See gtk_header_bar_set_subtitle().
  *
- * Returns: the subtitle of the header, or %NULL if none has
+ * Returns: (nullable): the subtitle of the header, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -1374,7 +1374,7 @@ gtk_header_bar_set_custom_title (GtkHeaderBar *bar,
  * Retrieves the custom title widget of the header. See
  * gtk_header_bar_set_custom_title().
  *
- * Returns: (transfer none): the custom title widget
+ * Returns: (nullable) (transfer none): the custom title widget
  *    of the header, or %NULL if none has been set explicitly.
  *
  * Since: 3.10

gtk/gtkicontheme.c

@@ -3624,7 +3624,7 @@ gtk_icon_info_get_base_scale (GtkIconInfo *icon_info)
  * filename if a builtin icon is returned; in this case, you should
  * use gtk_icon_info_get_builtin_pixbuf().
  * 
- * Returns: (type filename): the filename for the icon, or %NULL
+ * Returns: (nullable) (type filename): the filename for the icon, or %NULL
  *     if gtk_icon_info_get_builtin_pixbuf() should be used instead.
  *     The return value is owned by GTK+ and should not be modified
  *     or freed.

gtk/gtkiconview.c

@@ -4441,8 +4441,8 @@ gtk_icon_view_convert_widget_to_bin_window_coords (GtkIconView *icon_view,
  * See gtk_icon_view_convert_widget_to_bin_window_coords() for converting
  * widget coordinates to bin_window coordinates.
  * 
- * Returns: The #GtkTreePath corresponding to the icon or %NULL
+ * Returns: (nullable) (transfer full): The #GtkTreePath corresponding
- * if no icon exists at that position.
+ * to the icon or %NULL if no icon exists at that position.
  *
  * Since: 2.6 
  **/
@@ -5082,7 +5082,7 @@ gtk_icon_view_set_model (GtkIconView *icon_view,
  * Returns the model the #GtkIconView is based on.  Returns %NULL if the
  * model is unset.
  *
- * Returns: (transfer none): A #GtkTreeModel, or %NULL if none is
+ * Returns: (nullable) (transfer none): A #GtkTreeModel, or %NULL if none is
  *     currently being used.
  *
  * Since: 2.6 

gtk/gtkimage.c

@@ -1346,7 +1346,7 @@ gtk_image_get_storage_type (GtkImage *image)
  * The caller of this function does not own a reference to the
  * returned pixbuf.
  * 
- * Returns: (transfer none): the displayed pixbuf, or %NULL if
+ * Returns: (nullable) (transfer none): the displayed pixbuf, or %NULL if
  * the image is empty
  **/
 GdkPixbuf*
@@ -1433,7 +1433,7 @@ gtk_image_get_icon_set  (GtkImage        *image,
  * The caller of this function does not own a reference to the
  * returned animation.
  * 
- * Returns: (transfer none): the displayed animation, or %NULL if
+ * Returns: (nullable) (transfer none): the displayed animation, or %NULL if
  * the image is empty
  **/
 GdkPixbufAnimation*

gtk/gtklabel.c

@@ -2101,7 +2101,7 @@ gtk_label_set_mnemonic_widget (GtkLabel  *label,
  * Retrieves the target of the mnemonic (keyboard shortcut) of this
  * label. See gtk_label_set_mnemonic_widget().
  *
- * Returns: (transfer none): the target of the label’s mnemonic,
+ * Returns: (nullable) (transfer none): the target of the label’s mnemonic,
  *     or %NULL if none has been set and the default algorithm will be used.
  **/
 GtkWidget *
@@ -2322,7 +2322,7 @@ gtk_label_set_attributes (GtkLabel         *label,
  * effective attributes for the label, use
  * pango_layout_get_attribute (gtk_label_get_layout (label)).
  *
- * Returns: (transfer none): the attribute list, or %NULL
+ * Returns: (nullable) (transfer none): the attribute list, or %NULL
  *     if none was set.
  **/
 PangoAttrList *

gtk/gtkmain.c

@@ -313,7 +313,7 @@ gtk_get_interface_age (void)
  * old version of gtk_check_version(), but still get loaded
  * into an application using a newer version of GTK+.
  *
- * Returns: %NULL if the GTK+ library is compatible with the
+ * Returns: (nullable): %NULL if the GTK+ library is compatible with the
  *   given version, or a string describing the version mismatch.
  *   The returned string is owned by GTK+ and should not be modified
  *   or freed.

gtk/gtkmenubutton.c

@@ -823,7 +823,7 @@ gtk_menu_button_set_popup (GtkMenuButton *menu_button,
  * If the button does not use a #GtkMenu, this function
  * returns %NULL.
  *
- * Returns: (transfer none): a #GtkMenu or %NULL
+ * Returns: (nullable) (transfer none): a #GtkMenu or %NULL
  *
  * Since: 3.6
  */
@@ -905,7 +905,7 @@ gtk_menu_button_set_menu_model (GtkMenuButton *menu_button,
  *
  * Returns the #GMenuModel used to generate the popup.
  *
- * Returns: (transfer none): a #GMenuModel or %NULL
+ * Returns: (nullable) (transfer none): a #GMenuModel or %NULL
  *
  * Since: 3.6
  */
@@ -974,7 +974,7 @@ gtk_menu_button_set_align_widget (GtkMenuButton *menu_button,
  *
  * Returns the parent #GtkWidget to use to line up with menu.
  *
- * Returns: (transfer none): a #GtkWidget value or %NULL
+ * Returns: (nullable) (transfer none): a #GtkWidget value or %NULL
  *
  * Since: 3.6
  */
@@ -1220,7 +1220,7 @@ gtk_menu_button_set_popover (GtkMenuButton *menu_button,
  * If the button is not using a #GtkPopover, this function
  * returns %NULL.
  *
- * Returns: (transfer none): a #GtkPopover or %NULL
+ * Returns: (nullable) (transfer none): a #GtkPopover or %NULL
  *
  * Since: 3.12
  */

gtk/gtkmenuitem.c

@@ -1554,7 +1554,7 @@ gtk_menu_item_set_submenu (GtkMenuItem *menu_item,
  * Gets the submenu underneath this menu item, if any.
  * See gtk_menu_item_set_submenu().
  *
- * Returns: (transfer none): submenu for this menu item, or %NULL if none
+ * Returns: (nullable) (transfer none): submenu for this menu item, or %NULL if none
  */
 GtkWidget *
 gtk_menu_item_get_submenu (GtkMenuItem *menu_item)
@@ -2479,8 +2479,8 @@ gtk_menu_item_set_accel_path (GtkMenuItem *menu_item,
  *
  * See gtk_menu_item_set_accel_path() for details.
  *
- * Returns: the accelerator path corresponding to this menu
+ * Returns: (nullable) (transfer none): the accelerator path corresponding to
- *     item’s functionality, or %NULL if not set
+ *     this menu item’s functionality, or %NULL if not set
  *
  * Since: 2.14
  */

gtk/gtknativedialog.c

@@ -496,7 +496,7 @@ gtk_native_dialog_set_title (GtkNativeDialog *self,
  *
  * Gets the title of the #GtkNativeDialog.
  *
- * Returns: the title of the dialog, or %NULL if none has
+ * Returns: (nullable): the title of the dialog, or %NULL if none has
  *    been set explicitly. The returned string is owned by the widget
  *    and must not be modified or freed.
  *
@@ -546,8 +546,8 @@ gtk_native_dialog_set_transient_for (GtkNativeDialog *self,
  * Fetches the transient parent for this window. See
  * gtk_native_dialog_set_transient_for().
  *
- * Returns: (transfer none): the transient parent for this window, or %NULL
+ * Returns: (nullable) (transfer none): the transient parent for this window,
- *    if no transient parent has been set.
+ * or %NULL if no transient parent has been set.
  *
  * Since: 3.20
  **/

gtk/gtknotebook.c

@@ -7334,8 +7334,8 @@ gtk_notebook_get_current_page (GtkNotebook *notebook)
  *
  * Returns the child widget contained in page number @page_num.
  *
- * Returns: (transfer none): the child widget, or %NULL
+ * Returns: (nullable) (transfer none): the child widget, or %NULL if @page_num
- *     if @page_num is out of bounds
+ * is out of bounds
  */
 GtkWidget*
 gtk_notebook_get_nth_page (GtkNotebook *notebook,
@@ -8050,9 +8050,9 @@ gtk_notebook_set_tab_label_text (GtkNotebook *notebook,
  * Retrieves the text of the tab label for the page containing
  * @child.
  *
- * Returns: the text of the tab label, or %NULL if the
+ * Returns: (nullable): the text of the tab label, or %NULL if the tab label
- *     tab label widget is not a #GtkLabel. The string is owned
+ * widget is not a #GtkLabel. The string is owned by the widget and must not be
- *     by the widget and must not be freed.
+ * freed.
  */
 const gchar *
 gtk_notebook_get_tab_label_text (GtkNotebook *notebook,
@@ -8078,9 +8078,9 @@ gtk_notebook_get_tab_label_text (GtkNotebook *notebook,
  *
  * Retrieves the menu label widget of the page containing @child.
  *
- * Returns: (transfer none): the menu label, or %NULL if the
+ * Returns: (nullable) (transfer none): the menu label, or %NULL if the
- *     notebook page does not have a menu label other than the
+ * notebook page does not have a menu label other than the default (the tab
- *     default (the tab label).
+ * label).
  */
 GtkWidget*
 gtk_notebook_get_menu_label (GtkNotebook *notebook,
@@ -8185,10 +8185,10 @@ gtk_notebook_set_menu_label_text (GtkNotebook *notebook,
  * Retrieves the text of the menu label for the page containing
  * @child.
  *
- * Returns: the text of the tab label, or %NULL if the
+ * Returns: (nullable): the text of the tab label, or %NULL if the widget does
- *     widget does not have a menu label other than the default
+ * not have a menu label other than the default menu label, or the menu label
- *     menu label, or the menu label widget is not a #GtkLabel.
+ * widget is not a #GtkLabel. The string is owned by the widget and must not be
- *     The string is owned by the widget and must not be freed.
+ * freed.
  */
 const gchar *
 gtk_notebook_get_menu_label_text (GtkNotebook *notebook,
@@ -8411,8 +8411,7 @@ gtk_notebook_set_group_name (GtkNotebook *notebook,
  *
  * Gets the current group name for @notebook.
  *
- * Returns: (transfer none): the group name,
+ * Returns: (nullable) (transfer none): the group name, or %NULL if none is set
- *     or %NULL if none is set.
  *
  * Since: 2.24
  */
@@ -8597,8 +8596,8 @@ gtk_notebook_set_tab_detachable (GtkNotebook *notebook,
  *
  * Gets one of the action widgets. See gtk_notebook_set_action_widget().
  *
- * Returns: (transfer none): The action widget with the given @pack_type
+ * Returns: (nullable) (transfer none): The action widget with the given
- *     or %NULL when this action widget has not been set
+ * @pack_type or %NULL when this action widget has not been set
  *
  * Since: 2.20
  */

gtk/gtkoffscreenwindow.c

@@ -297,7 +297,7 @@ gtk_offscreen_window_new (void)
  * a #cairo_surface_t.  If you need to keep this around over window
  * resizes then you should add a reference to it.
  *
- * Returns: (transfer none): A #cairo_surface_t pointer to the offscreen
+ * Returns: (nullable) (transfer none): A #cairo_surface_t pointer to the offscreen
  *     surface, or %NULL.
  *
  * Since: 2.20
@@ -319,7 +319,7 @@ gtk_offscreen_window_get_surface (GtkOffscreenWindow *offscreen)
  * and the application should unreference it once it is no longer
  * needed.
  *
- * Returns: (transfer full): A #GdkPixbuf pointer, or %NULL.
+ * Returns: (nullable) (transfer full): A #GdkPixbuf pointer, or %NULL.
  *
  * Since: 2.20
  */

gtk/gtkpaned.c

@@ -2362,7 +2362,7 @@ gtk_paned_set_position (GtkPaned *paned,
  * 
  * Obtains the first child of the paned widget.
  * 
- * Returns: (transfer none): first child, or %NULL if it is not set.
+ * Returns: (nullable) (transfer none): first child, or %NULL if it is not set.
  *
  * Since: 2.4
  **/
@@ -2380,7 +2380,7 @@ gtk_paned_get_child1 (GtkPaned *paned)
  * 
  * Obtains the second child of the paned widget.
  * 
- * Returns: (transfer none): second child, or %NULL if it is not set.
+ * Returns: (nullable) (transfer none): second child, or %NULL if it is not set.
  *
  * Since: 2.4
  **/

gtk/gtkplacessidebar.c

@@ -4608,8 +4608,8 @@ gtk_places_sidebar_set_location (GtkPlacesSidebar *sidebar,
  * function to get the location that is being referred to during the callbacks
  * for your menu items.
  *
- * Returns: (transfer full): a GFile with the selected location, or #NULL if nothing is visually
+ * Returns: (nullable) (transfer full): a GFile with the selected location, or
- * selected.
+ * %NULL if nothing is visually selected.
  *
  * Since: 3.10
  */
@@ -5096,9 +5096,9 @@ gtk_places_sidebar_list_shortcuts (GtkPlacesSidebar *sidebar)
  * and returns one of them.  This function is used by #GtkFileChooser to implement
  * the “Alt-1”, “Alt-2”, etc. shortcuts, which activate the cooresponding bookmark.
  *
- * Returns: (transfer full): The bookmark specified by the index @n, or
+ * Returns: (nullable) (transfer full): The bookmark specified by the index @n, or
- * #NULL if no such index exist.  Note that the indices start at 0, even though
+ * %NULL if no such index exist.  Note that the indices start at 0, even though
- * the file chooser starts them with the keyboard shortcut “Alt-1”.
+ * the file chooser starts them with the keyboard shortcut "Alt-1".
  *
  * Since: 3.10
  */

gtk/gtkplug.c

@@ -379,7 +379,7 @@ gtk_plug_get_embedded (GtkPlug *plug)
  *
  * Retrieves the socket the plug is embedded in.
  *
- * Returns: (transfer none): the window of the socket, or %NULL
+ * Returns: (nullable) (transfer none): the window of the socket, or %NULL
  *
  * Since: 2.14
  **/

gtk/gtkpopover.c

@@ -2511,7 +2511,8 @@ gtk_popover_set_default_widget (GtkPopover *popover,
  * Gets the widget that should be set as the default while
  * the popover is shown.
  *
- * Returns: (transfer none): the default widget, or %NULL if there is none
+ * Returns: (nullable) (transfer none): the default widget,
+ * or %NULL if there is none
  *
  * Since: 3.18
  */

gtk/gtkprogressbar.c

@@ -1643,7 +1643,7 @@ gtk_progress_bar_set_inverted (GtkProgressBar *pbar,
  * to the text, not a copy of it, so will become invalid
  * if you change the text in the progress bar.
  *
- * Returns: text, or %NULL; this string is owned by the widget
+ * Returns: (nullable): text, or %NULL; this string is owned by the widget
  * and should not be modified or freed.
  */
 const gchar*

gtk/gtkrecentfilter.c

@@ -463,7 +463,7 @@ gtk_recent_filter_set_name (GtkRecentFilter *filter,
  * Gets the human-readable name for the filter.
  * See gtk_recent_filter_set_name().
  *
- * Returns: the name of the filter, or %NULL.  The returned string
+ * Returns: (nullable): the name of the filter, or %NULL.  The returned string
  *   is owned by the filter object and should not be freed.
  *
  * Since: 2.10

gtk/gtkrecentmanager.c

@@ -1162,7 +1162,7 @@ build_recent_info (GBookmarkFile *bookmarks,
  * returns a #GtkRecentInfo-struct containing informations about the resource
  * like its MIME type, or its display name.
  *
- * Returns: a #GtkRecentInfo-struct containing information
+ * Returns: (nullable): a #GtkRecentInfo-struct containing information
  *   about the resource pointed by @uri, or %NULL if the URI was
  *   not registered in the recently used resources list. Free with
  *   gtk_recent_info_unref().

gtk/gtksettings.c

@@ -1903,8 +1903,8 @@ gtk_settings_get_for_screen (GdkScreen *screen)
  * Gets the #GtkSettings object for the default GDK screen, creating
  * it if necessary. See gtk_settings_get_for_screen().
  *
- * Returns: (transfer none): a #GtkSettings object. If there is no default
+ * Returns: (nullable) (transfer none): a #GtkSettings object. If there is
- *  screen, then returns %NULL.
+ * no default screen, then returns %NULL.
  **/
 GtkSettings*
 gtk_settings_get_default (void)

gtk/gtksocket.c

@@ -369,7 +369,8 @@ gtk_socket_get_id (GtkSocket *socket)
  * Retrieves the window of the plug. Use this to check if the plug has
  * been created inside of the socket.
  *
- * Returns: (transfer none): the window of the plug if available, or %NULL
+ * Returns: (nullable) (transfer none): the window of the plug if
+ * available, or %NULL
  *
  * Since:  2.14
  **/

gtk/gtkstacksidebar.c

@@ -522,7 +522,7 @@ gtk_stack_sidebar_set_stack (GtkStackSidebar *sidebar,
  * Retrieves the stack.
  * See gtk_stack_sidebar_set_stack().
  *
- * Returns: (transfer full): the associated #GtkStack or
+ * Returns: (nullable) (transfer full): the associated #GtkStack or
  *     %NULL if none has been set explicitly
  *
  * Since: 3.16

gtk/gtkstackswitcher.c

@@ -436,7 +436,7 @@ gtk_stack_switcher_set_stack (GtkStackSwitcher *switcher,
  * Retrieves the stack.
  * See gtk_stack_switcher_set_stack().
  *
- * Returns: (transfer none): the stack, or %NULL if
+ * Returns: (nullable) (transfer none): the stack, or %NULL if
  *    none has been set explicitly.
  *
  * Since: 3.10

gtk/gtkstylecontext.c

@@ -751,7 +751,8 @@ gtk_style_context_remove_provider_for_screen (GdkScreen        *screen,
  * Shorthand CSS properties cannot be queried for a location and will
  * always return %NULL.
  *
- * Returns: %NULL or the section where value was defined
+ * Returns: (nullable) (transfer none): %NULL or the section where a value
+ * for @property was defined
  **/
 GtkCssSection *
 gtk_style_context_get_section (GtkStyleContext *context,
@@ -1180,7 +1181,7 @@ gtk_style_context_set_parent (GtkStyleContext *context,
  * Gets the parent context set via gtk_style_context_set_parent().
  * See that function for details.
  *
- * Returns: (transfer none): the parent context or %NULL
+ * Returns: (nullable) (transfer none): the parent context or %NULL
  *
  * Since: 3.4
  **/
@@ -2026,7 +2027,7 @@ gtk_style_context_set_frame_clock (GtkStyleContext *context,
  *
  * Returns the #GdkFrameClock to which @context is attached.
  *
- * Returns: (transfer none): a #GdkFrameClock, or %NULL
+ * Returns: (nullable) (transfer none): a #GdkFrameClock, or %NULL
  *  if @context does not have an attached frame clock.
  *
  * Since: 3.8

gtk/gtktestutils.c

@@ -439,7 +439,7 @@ gtk_test_find_sibling (GtkWidget *base_widget,
  * gtk_test_widget_click() for possible caveats involving the search of
  * such widgets and synthesizing widget events.
  *
- * Returns: (transfer none): a valid widget if any is found or %NULL.
+ * Returns: (nullable) (transfer none): a valid widget if any is found or %NULL.
  *
  * Since: 2.14
  **/

gtk/gtktextbuffer.c

@@ -2251,7 +2251,7 @@ gtk_text_buffer_delete_mark (GtkTextBuffer *buffer,
  * Returns the mark named @name in buffer @buffer, or %NULL if no such
  * mark exists in the buffer.
  *
- * Returns: (transfer none): a #GtkTextMark, or %NULL
+ * Returns: (nullable) (transfer none): a #GtkTextMark, or %NULL
  **/
 GtkTextMark*
 gtk_text_buffer_get_mark (GtkTextBuffer *buffer,

gtk/gtktextbufferrichtext.h

@@ -40,8 +40,8 @@ G_BEGIN_DECLS
  * A function that is called to serialize the content of a text buffer.
  * It must return the serialized form of the content.
  *
- * Returns: a newly-allocated array of guint8 which contains the serialized
+ * Returns: (nullable): a newly-allocated array of guint8 which contains
- *   data, or %NULL if an error occurred
+ * the serialized data, or %NULL if an error occurred
  */
 typedef guint8 * (* GtkTextBufferSerializeFunc)   (GtkTextBuffer     *register_buffer,
                                                    GtkTextBuffer     *content_buffer,

gtk/gtktexttagtable.c

@@ -289,7 +289,8 @@ gtk_text_tag_table_add (GtkTextTagTable *table,
  * 
  * Look up a named tag.
  * 
- * Returns: (transfer none): The tag, or %NULL if none by that name is in the table.
+ * Returns: (nullable) (transfer none): The tag, or %NULL if none by that
+ * name is in the table.
  **/
 GtkTextTag*
 gtk_text_tag_table_lookup (GtkTextTagTable *table,

gtk/gtktextview.c

@@ -3460,8 +3460,8 @@ gtk_text_view_set_tabs (GtkTextView   *text_view,
  * “standard” (8-space) tabs are used. Free the return value
  * with pango_tab_array_free().
  * 
- * Returns: copy of default tab array, or %NULL if “standard” 
+ * Returns: (nullable) (transfer full): copy of default tab array, or %NULL if
- *    tabs are used; must be freed with pango_tab_array_free().
+ *    “standard" tabs are used; must be freed with pango_tab_array_free().
  **/
 PangoTabArray*
 gtk_text_view_get_tabs (GtkTextView *text_view)
@@ -10206,7 +10206,7 @@ text_window_get_height (GtkTextWindow *win)
  * height is 0, and are nonexistent before the widget has been
  * realized.
  *
- * Returns: (transfer none): a #GdkWindow, or %NULL
+ * Returns: (nullable) (transfer none): a #GdkWindow, or %NULL
  **/
 GdkWindow*
 gtk_text_view_get_window (GtkTextView *text_view,

gtk/gtktoolbar.c

@@ -2937,7 +2937,7 @@ gtk_toolbar_get_n_items (GtkToolbar *toolbar)
  * Returns the @n'th item on @toolbar, or %NULL if the
  * toolbar does not contain an @n'th item.
  *
- * Returns: (transfer none): The @n'th #GtkToolItem on @toolbar,
+ * Returns: (nullable) (transfer none): The @n'th #GtkToolItem on @toolbar,
  *     or %NULL if there isn’t an @n'th item.
  *
  * Since: 2.4

gtk/gtktoolbutton.c

@@ -1217,7 +1217,7 @@ gtk_tool_button_set_label (GtkToolButton *button,
  * doesn’t have a label. or uses a the label from a stock item. The returned
  * string is owned by GTK+, and must not be modified or freed.
  * 
- * Returns: The label, or %NULL
+ * Returns: (nullable): The label, or %NULL
  * 
  * Since: 2.4
  **/
@@ -1372,7 +1372,7 @@ gtk_tool_button_set_icon_name (GtkToolButton *button,
  * Returns the name of the themed icon for the tool button,
  * see gtk_tool_button_set_icon_name().
  *
- * Returns: the icon name or %NULL if the tool button has
+ * Returns: (nullable): the icon name or %NULL if the tool button has
  * no themed icon
  *
  * Since: 2.8
@@ -1478,7 +1478,7 @@ gtk_tool_button_set_label_widget (GtkToolButton *button,
  * Returns the widget used as label on @button.
  * See gtk_tool_button_set_label_widget().
  *
- * Returns: (transfer none): The widget used as label
+ * Returns: (nullable) (transfer none): The widget used as label
  *     on @button, or %NULL.
  *
  * Since: 2.4
@@ -1498,7 +1498,7 @@ gtk_tool_button_get_label_widget (GtkToolButton *button)
  * Return the widget used as icon widget on @button.
  * See gtk_tool_button_set_icon_widget().
  *
- * Returns: (transfer none): The widget used as icon
+ * Returns: (nullable) (transfer none): The widget used as icon
  *     on @button, or %NULL.
  *
  * Since: 2.4

gtk/gtktoolpalette.c

@@ -1489,7 +1489,7 @@ gtk_tool_palette_get_expand (GtkToolPalette   *palette,
  * Gets the item at position (x, y).
  * See gtk_tool_palette_get_drop_group().
  *
- * Returns: (transfer none): the #GtkToolItem at position or %NULL if there is no such item
+ * Returns: (nullable) (transfer none): the #GtkToolItem at position or %NULL if there is no such item
  *
  * Since: 2.20
  */
@@ -1521,8 +1521,8 @@ gtk_tool_palette_get_drop_item (GtkToolPalette *palette,
  *
  * Gets the group at position (x, y).
  *
- * Returns: (transfer none): the #GtkToolItemGroup at position or %NULL
+ * Returns: (nullable) (transfer none): the #GtkToolItemGroup at position
- *     if there is no such group
+ * or %NULL if there is no such group
  *
  * Since: 2.20
  */

gtk/gtktreemodelfilter.c

@@ -4128,7 +4128,7 @@ gtk_real_tree_model_filter_convert_child_path_to_path (GtkTreeModelFilter *filte
  * child model or points to a row which is not visible in @filter, then %NULL
  * is returned.
  *
- * Returns: A newly allocated #GtkTreePath, or %NULL.
+ * Returns: (nullable) (transfer full): A newly allocated #GtkTreePath, or %NULL.
  *
  * Since: 2.4
  */
@@ -4171,7 +4171,7 @@ gtk_tree_model_filter_convert_child_path_to_path (GtkTreeModelFilter *filter,
  * point to the same location in the model not being filtered. If @filter_path
  * does not point to a location in the child model, %NULL is returned.
  *
- * Returns: A newly allocated #GtkTreePath, or %NULL.
+ * Returns: (nullable) (transfer full): A newly allocated #GtkTreePath, or %NULL.
  *
  * Since: 2.4
  */

gtk/gtktreemodelsort.c

@@ -2289,7 +2289,7 @@ gtk_real_tree_model_sort_convert_child_path_to_path (GtkTreeModelSort *tree_mode
  * point to the same row in the sorted model.  If @child_path isn’t a valid 
  * path on the child model, then %NULL is returned.
  * 
- * Returns: A newly allocated #GtkTreePath, or %NULL
+ * Returns: (nullable) (transfer full): A newly allocated #GtkTreePath, or %NULL
  **/
 GtkTreePath *
 gtk_tree_model_sort_convert_child_path_to_path (GtkTreeModelSort *tree_model_sort,
@@ -2362,7 +2362,7 @@ gtk_tree_model_sort_convert_child_iter_to_iter (GtkTreeModelSort *tree_model_sor
  * sorted.  If @sorted_path does not point to a location in the child model, 
  * %NULL is returned.
  * 
- * Returns: A newly allocated #GtkTreePath, or %NULL
+ * Returns: (nullable) (transfer full): A newly allocated #GtkTreePath, or %NULL
  **/
 GtkTreePath *
 gtk_tree_model_sort_convert_path_to_child_path (GtkTreeModelSort *tree_model_sort,

gtk/gtktreeview.c

@@ -12256,8 +12256,8 @@ gtk_tree_view_get_n_columns (GtkTreeView *tree_view)
  *
  * Gets the #GtkTreeViewColumn at the given position in the #tree_view.
  *
- * Returns: (transfer none): The #GtkTreeViewColumn, or %NULL if the
+ * Returns: (nullable) (transfer none): The #GtkTreeViewColumn, or %NULL if the
- *     position is outside the range of columns.
+ * position is outside the range of columns.
  **/
 GtkTreeViewColumn *
 gtk_tree_view_get_column (GtkTreeView *tree_view,
@@ -13444,8 +13444,8 @@ gtk_tree_view_set_cursor_on_cell (GtkTreeView       *tree_view,
  * This is used primarily to compare to `event->window`
  * to confirm that the event on @tree_view is on the right window.
  *
- * Returns: (transfer none): A #GdkWindow, or %NULL when @tree_view
+ * Returns: (nullable) (transfer none): A #GdkWindow, or %NULL when @tree_view
- *     hasn’t been realized yet
+ * hasn’t been realized yet.
  **/
 GdkWindow *
 gtk_tree_view_get_bin_window (GtkTreeView *tree_view)

gtk/gtktreeviewcolumn.c

@@ -2520,7 +2520,7 @@ gtk_tree_view_column_set_widget (GtkTreeViewColumn *tree_column,
  * Returns the #GtkWidget in the button on the column header.
  * If a custom widget has not been set then %NULL is returned.
  *
- * Returns: (transfer none): The #GtkWidget in the column
+ * Returns: (nullable) (transfer none): The #GtkWidget in the column
  *     header, or %NULL
  **/
 GtkWidget *
@@ -3101,7 +3101,7 @@ gtk_tree_view_column_queue_resize (GtkTreeViewColumn *tree_column)
  * If @column is currently not inserted in any tree view, %NULL is
  * returned.
  *
- * Returns: (transfer none): The tree view wherein @column has
+ * Returns: (nullable) (transfer none): The tree view wherein @column has
  *     been inserted if any, %NULL otherwise.
  *
  * Since: 2.12

gtk/gtkwidget.c

@@ -5766,7 +5766,8 @@ gtk_widget_queue_resize_no_redraw (GtkWidget *widget)
  *
  * Unrealized widgets do not have a frame clock.
  *
- * Returns: (transfer none): a #GdkFrameClock (or #NULL if widget is unrealized)
+ * Returns: (nullable) (transfer none): a #GdkFrameClock,
+ * or #NULL if widget is unrealized
  *
  * Since: 3.8
  */

gtk/gtkwindowgroup.c

@@ -337,7 +337,7 @@ _gtk_window_group_remove_device_grab (GtkWindowGroup *window_group,
  *
  * Returns the current grab widget for @device, or %NULL if none.
  *
- * Returns: (transfer none): The grab widget, or %NULL
+ * Returns: (nullable) (transfer none): The grab widget, or %NULL
  *
  * Since: 3.0
  */