fix module build failed error at Linter.parseResults

src/Linter.js

@@ -113,10 +113,12 @@ export default class Linter {
 
   parseResults({ results }) {
     // add filename for each results so formatter can have relevant filename
-    results.forEach((r) => {
-      // eslint-disable-next-line no-param-reassign
-      r.filePath = this.loaderContext.resourcePath;
-    });
+    if (results) {
+      results.forEach((r) => {
+        // eslint-disable-next-line no-param-reassign
+        r.filePath = this.loaderContext.resourcePath;
+      });
+    }
 
     return results;
   }

test/Linter.test.js

@@ -0,0 +1,22 @@
+import Linter from '../src/Linter';
+
+const loaderContext = { resourcePath: 'test' };
+const options = {
+  eslintPath: 'eslint',
+  ignore: false,
+  formatter: jest.fn(),
+};
+const res = { results: [{ filePath: '' }] };
+
+describe('Linter', () => {
+  const linter = new Linter(loaderContext, options);
+
+  it('should parse undefined results without error', () => {
+    // eslint-disable-next-line no-undefined
+    expect(linter.parseResults({})).toEqual(undefined);
+  });
+
+  it('should parse results correctly', () => {
+    expect(linter.parseResults(res)).toEqual([{ filePath: 'test' }]);
+  });
+});