core: remove NO_ERROR from default responses

lighthouse-core/runner.js

@@ -331,7 +331,7 @@ class Runner {
   /**
    * Returns first runtimeError found in artifacts.
    * @param {LH.Artifacts} artifacts
-   * @return {LH.Result['runtimeError']}
+   * @return {LH.Result['runtimeError']|undefined}
    */
   static getArtifactRuntimeError(artifacts) {
     for (const possibleErrorArtifact of Object.values(artifacts)) {
@@ -345,10 +345,7 @@ class Runner {
       }
     }
 
-    return {
-      code: LHError.NO_ERROR,
-      message: '',
-    };
+    return undefined;
   }
 
   /**

lighthouse-core/test/results/sample_v2.json

@@ -10,10 +10,6 @@
   "requestedUrl": "http://localhost:10200/dobetterweb/dbw_tester.html",
   "finalUrl": "http://localhost:10200/dobetterweb/dbw_tester.html",
   "runWarnings": [],
-  "runtimeError": {
-    "code": "NO_ERROR",
-    "message": ""
-  },
   "audits": {
     "is-on-https": {
       "id": "is-on-https",

lighthouse-core/test/runner-test.js

@@ -112,6 +112,21 @@ describe('Runner', () => {
       }
     });
 
+    it('does not include a top-level runtimeError when gatherers were successful', async () => {
+      const config = new Config({
+        settings: {
+          auditMode: __dirname + '/fixtures/artifacts/perflog/',
+
+        },
+        audits: [
+          'content-width',
+        ],
+      });
+
+      const {lhr} = await Runner.run(undefined, {config});
+      assert.strictEqual(lhr.runtimeError, undefined);
+    });
+
     it('-GA is a normal run but it saves artifacts to disk', () => {
       const settings = {auditMode: artifactsPath, gatherMode: artifactsPath};
       const opts = {url, config: generateConfig(settings), driverMock};

types/lhr.d.ts

@@ -53,7 +53,7 @@ declare global {
       /** List of top-level warnings for this Lighthouse run. */
       runWarnings: string[];
       /** A top-level error message that, if present, indicates a serious enough problem that this Lighthouse result may need to be discarded. */
-      runtimeError: {code: string, message: string};
+      runtimeError?: {code: string, message: string};
       /** The User-Agent string of the browser used run Lighthouse for these results. */
       userAgent: string;
       /** Information about the environment in which Lighthouse was run. */