Emit null instead of empty object for validateAshHooks

This was left to minimize report.json changes in earlier
refactoring. Fixing it now should only affect the report.json
structure but not report.html.

lib/validator.js

@@ -186,16 +186,13 @@ const ashnazgHookUrls = [
 ];
 
 function validateAshHooks(hooks) {
-  // Note: unlike `reportError` used above, here empty object literals are
-  // pushed instead of nulls. This is simply to match the original structure
-  // of report.json. TODO: change this to null, or add error details.
   const errors = [];
   const ashHooks = hooks.filter(h => ashnazgHookUrls.includes(h.config.url) && h.config.contentType === "json" && h.config.insecureSsl === "0" && h.config.secret !== "");
   if (ashHooks.length === 0) {
-    errors.push(['missingashnazghook', {}]);
+    errors.push(['missingashnazghook', null]);
   }
   if (ashHooks.length > 1) {
-    errors.push(['duplicateashnazghooks', {}]);
+    errors.push(['duplicateashnazghooks', null]);
   }
   return errors;
 }

test/validator.js

@@ -411,7 +411,7 @@ describe('validateAshHooks', () => {
   it('no hooks', () => {
     const hooks = [];
     const errors = validateAshHooks(hooks);
-    assert.deepStrictEqual(errors, [['missingashnazghook', {}]]);
+    assert.deepStrictEqual(errors, [['missingashnazghook', null]]);
   });
 
   it('one hook', () => {
@@ -444,6 +444,6 @@ describe('validateAshHooks', () => {
       }
     }];
     const errors = validateAshHooks(hooks);
-    assert.deepStrictEqual(errors, [['duplicateashnazghooks', {}]]);
+    assert.deepStrictEqual(errors, [['duplicateashnazghooks', null]]);
   });
 });