Return empty object rather than 404 error

src/wp-includes/rest-api/endpoints/class-wp-rest-templates-controller.php

@@ -153,7 +153,6 @@ public function register_routes() {
 	 *
 	 * @since 6.1.0
 	 * @since 6.3.0 Ignore empty templates.
-	 * @since 6.5.3 Return a 404 error if no fallback templates are found.
 	 *
 	 * @param WP_REST_Request $request The request instance.
 	 * @return WP_REST_Response|WP_Error
@@ -166,11 +165,8 @@ public function get_template_fallback( $request ) {
 			array_shift( $hierarchy );
 		} while ( ! empty( $hierarchy ) && empty( $fallback_template->content ) );
 
-		if ( ! $fallback_template ) {
-			return new WP_Error( 'rest_template_not_found', __( 'No fallback templates exist for that slug.' ), array( 'status' => 404 ) );
-		}
-
-		$response = $this->prepare_item_for_response( $fallback_template, $request );
+		// To maintain original behavior, return an empty object rather than a 404 error when no template is found.
+		$response = $fallback_template ? $this->prepare_item_for_response( $fallback_template, $request ) : new stdClass();
 
 		return rest_ensure_response( $response );
 	}

tests/phpunit/tests/rest-api/wpRestTemplatesController.php

@@ -918,7 +918,8 @@ public function test_get_template_fallback_not_found() {
 		$request = new WP_REST_Request( 'GET', '/wp/v2/templates/lookup' );
 		$request->set_param( 'slug', 'not-found' );
 		$response = rest_get_server()->dispatch( $request );
-		$this->assertErrorResponse( 'rest_template_not_found', $response, 404 );
+		$data     = $response->get_data();
+		$this->assertEquals( new stdClass(), $data, 'Response should be an empty object when a fallback template is not found.' );
 	}
 
 	/**