Widgets editor: Fix error when saving empty Legacy Widget block (#32359)

Author: noisysocks

packages/edit-widgets/src/store/transformers.js

@@ -37,7 +37,11 @@ export function transformWidgetToBlock( widget ) {
 export function transformBlockToWidget( block, relatedWidget = {} ) {
 	let widget;
 
-	if ( block.name === 'core/legacy-widget' ) {
+	const isValidLegacyWidgetBlock =
+		block.name === 'core/legacy-widget' &&
+		( block.attributes.id || block.attributes.instance );
+
+	if ( isValidLegacyWidgetBlock ) {
 		widget = {
 			...relatedWidget,
 			id: block.attributes.id ?? relatedWidget.id,
@@ -56,13 +60,6 @@ export function transformBlockToWidget( block, relatedWidget = {} ) {
 		};
 	}
 
-	// Delete deprecated properties.
-	delete widget.description;
-	delete widget.name;
-	delete widget.number;
-	delete widget.settings;
-	delete widget.widget_class;
-
 	// Delete read-only properties.
 	delete widget.rendered;
 	delete widget.rendered_form;