Better fix

tools/editor/plugins/mesh_editor_plugin.cpp

@@ -32,6 +32,8 @@ void MeshInstanceEditor::_menu_option(int p_option) {
 
 	Ref<Mesh> mesh = node->get_mesh();
 	if (mesh.is_null()) {
+		err_dialog->set_text("Mesh is empty!");
+		err_dialog->popup_centered(Size2(100,80));
 		return;
 	}
 
@@ -238,6 +240,9 @@ MeshInstanceEditor::MeshInstanceEditor() {
 	add_child(outline_dialog);
 	outline_dialog->connect("confirmed",this,"_create_outline_mesh");
 
+	err_dialog = memnew( AcceptDialog );
+	add_child(err_dialog);
+
 }