better null fix

Author: brendankenny

lighthouse-core/test/gather/gather-runner-test.js

@@ -27,7 +27,7 @@ jest.mock('../../lib/stack-collector.js', () => () => Promise.resolve([]));
  * @param {(...args: TParams) => TReturn} fn
  */
 function makeParamsOptional(fn) {
-  return /** @type {(...args: Nullable<RecursivePartial<TParams>>) => TReturn} */ (fn);
+  return /** @type {(...args: RecursivePartial<TParams>) => TReturn} */ (fn);
 }
 
 const GatherRunner = {
@@ -54,7 +54,13 @@ const GatherRunner = {
  */
 function makeConfig(json) {
   // @ts-expect-error: allow recursive partial.
-  return new Config(json);
+  const config = new Config(json);
+
+  // Since the config is for `gather-runner`, ensure it has `passes`.
+  if (!config.passes) {
+    throw new Error('gather-runner test configs must have `passes`');
+  }
+  return /** @type {Config & {passes: Array<LH.Config.Pass>}} */ (config);
 }
 
 const LoadFailureMode = {

types/externs.d.ts

@@ -50,11 +50,6 @@ declare global {
     [P in K]: P;
   };
 
-  /** Make all properties in T nullable. */
-  type Nullable<T> = {
-    [K in keyof T]: T[K] | null;
-  }
-
   /** Make optional all properties on T and any properties on object properties of T. */
   type RecursivePartial<T> = {
     [P in keyof T]+?: