set hasteImplModulePath to undefined, not null

Author: SimenB

packages/jest-config/src/normalize.ts

@@ -646,14 +646,16 @@ export default function normalize(
         case 'haste':
           value = {...oldOptions[key]};
           if (value.hasteImplModulePath != null) {
-            value.hasteImplModulePath = resolve(newOptions.resolver, {
+            const resolvedHasteImpl = resolve(newOptions.resolver, {
               filePath: replaceRootDirInPath(
                 options.rootDir,
                 value.hasteImplModulePath,
               ),
               key: 'haste.hasteImplModulePath',
               rootDir: options.rootDir,
             });
+
+            value.hasteImplModulePath = resolvedHasteImpl || undefined;
           }
           break;
         case 'projects':