Fix handling of nulls in some editors

editor/plugins/canvas_item_editor_plugin.cpp

@@ -3990,6 +3990,10 @@ void CanvasItemEditor::_selection_changed() {
 }
 
 void CanvasItemEditor::edit(CanvasItem *p_canvas_item) {
+	if (!p_canvas_item) {
+		return;
+	}
+
 	Array selection = editor_selection->get_selected_nodes();
 	if (selection.size() != 1 || Object::cast_to<Node>(selection[0]) != p_canvas_item) {
 		_reset_drag();

editor/plugins/theme_editor_plugin.cpp

@@ -3335,8 +3335,10 @@ void ThemeTypeEditor::set_edited_theme(const Ref<Theme> &p_theme) {
 	}
 
 	edited_theme = p_theme;
-	edited_theme->connect("changed", callable_mp(this, &ThemeTypeEditor::_update_type_list_debounced));
-	_update_type_list();
+	if (edited_theme.is_valid()) {
+		edited_theme->connect("changed", callable_mp(this, &ThemeTypeEditor::_update_type_list_debounced));
+		_update_type_list();
+	}
 
 	add_type_dialog->set_edited_theme(edited_theme);
 }
@@ -3496,7 +3498,9 @@ void ThemeEditor::edit(const Ref<Theme> &p_theme) {
 		preview_tab->set_preview_theme(p_theme);
 	}
 
-	theme_name->set_text(TTR("Theme:") + " " + theme->get_path().get_file());
+	if (theme.is_valid()) {
+		theme_name->set_text(TTR("Theme:") + " " + theme->get_path().get_file());
+	}
 }
 
 Ref<Theme> ThemeEditor::get_edited_theme() {