Add a few missing (nullable) annotations

gtk/gtkbutton.c

@@ -1417,7 +1417,7 @@ gtk_button_new_with_label (const gchar *label)
 
 /**
  * gtk_button_new_from_icon_name:
- * @icon_name: an icon name
+ * @icon_name: (nullable): an icon name or %NULL
  * @size: (type int): an icon size (#GtkIconSize)
  *
  * Creates a new button containing an icon from the current icon theme.

gtk/gtkgesture.c

@@ -1523,12 +1523,12 @@ _gtk_gesture_check (GtkGesture *gesture)
 /**
  * gtk_gesture_handles_sequence:
  * @gesture: a #GtkGesture
- * @sequence: a #GdkEventSequence
+ * @sequence: (nullable): a #GdkEventSequence or %NULL
  *
  * Returns %TRUE if @gesture is currently handling events corresponding to
  * @sequence.
  *
- * Returns: %TRUE if @gesture is handling @sequence
+ * Returns: %TRUE if @gesture is handling @sequence, %FALSE otherwise
  *
  * Since: 3.14
  **/

gtk/gtkimage.c

@@ -1284,7 +1284,7 @@ gtk_image_set_from_gicon  (GtkImage       *image,
 /**
  * gtk_image_set_from_surface:
  * @image: a #GtkImage
- * @surface: a cairo_surface_t
+ * @surface: (nullable): a cairo_surface_t or %NULL
  *
  * See gtk_image_new_from_surface() for details.
  *