Add non-nullable modifier to return type of functions never returning null.
@@ -31,7 +31,7 @@ function compareResults(expected, actual) {
/**
* @param {VALUE} result
* @param {number} millis
- * @return {Promise<VALUE>}
+ * @return {!Promise<VALUE>}
* @template VALUE
*/
function resolveAfterWaiting(result, millis) {
