[enzyme-adapter-react-16] [fix] isEmptyRender: properly detect memoized SFCs returning null

Fixes #2377.

Author: ljharb

packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js

@@ -250,7 +250,7 @@ function toTree(vnode) {
     case FiberTags.MemoSFC: {
       let renderedNodes = flatten(nodeAndSiblingsArray(node.child).map(toTree));
       if (renderedNodes.length === 0) {
-        renderedNodes = [node.memoizedProps.children];
+        renderedNodes = childrenToTree(node.memoizedProps.children);
       }
       return {
         nodeType: 'function',

packages/enzyme-test-suite/test/shared/methods/isEmptyRender.jsx

@@ -11,6 +11,7 @@ import { is } from '../../_helpers/version';
 
 import {
   createClass,
+  memo,
 } from '../../_helpers/react-compat';
 
 export default function describeIsEmptyRender({
@@ -178,5 +179,12 @@ export default function describeIsEmptyRender({
       expect(elements).to.have.lengthOf(3);
       expect(elements.isEmptyRender()).to.equal(!isShallow);
     });
+
+    it('works on a memoized functional component', () => {
+      const Component = memo(() => null);
+      const wrapper = Wrap(<Component />);
+      expect(wrapper.debug()).to.equal(isShallow ? '' : '<Memo() />');
+      expect(wrapper.isEmptyRender()).to.equal(true);
+    });
   });
 }