Add a null type test for memo (#14325)

Author: springuper

packages/react-reconciler/src/__tests__/ReactMemo-test.internal.js

@@ -306,13 +306,21 @@ describe('memo', () => {
         expect(ReactNoop.getChildren()).toEqual([span(20)]);
       });
 
-      it('warns if first argument is undefined', () => {
+      it('warns if the first argument is undefined', () => {
         expect(() => memo()).toWarnDev(
           'memo: The first argument must be a component. Instead ' +
             'received: undefined',
           {withoutStack: true},
         );
       });
+
+      it('warns if the first argument is null', () => {
+        expect(() => memo(null)).toWarnDev(
+          'memo: The first argument must be a component. Instead ' +
+            'received: null',
+          {withoutStack: true},
+        );
+      });
     });
   }
 });

scripts/jest/matchers/toWarnDev.js

@@ -130,7 +130,7 @@ const createMatcherFor = consoleMethod =>
       };
 
       // TODO Decide whether we need to support nested toWarn* expectations.
-      // If we don't need id, add a check here to see if this is already our spy,
+      // If we don't need it, add a check here to see if this is already our spy,
       // And throw an error.
       const originalMethod = console[consoleMethod];