Update warning message

Author: jerelmiller

src/link/local-resolvers/LocalResolversLink.ts

@@ -324,7 +324,7 @@ export class LocalResolversLink extends ApolloLink {
 
       if (result === undefined) {
         invariant.warn(
-          "The '%s' resolver returned `undefined` instead of a value. This is likely a bug in the resolver. Return `null` instead if you didn't mean to return a value.",
+          "The '%s' resolver returned `undefined` instead of a value. This is likely a bug in the resolver. If you didn't mean to return a value, use return `null` instead.",
           getResolverName(typename, fieldName)
         );
         result = null;

src/link/local-resolvers/__tests__/LocalResolversLink/base.test.ts

@@ -523,7 +523,7 @@ test("warns when a resolver returns undefined and sets value to null", async ()
 
   expect(console.warn).toHaveBeenCalledTimes(1);
   expect(console.warn).toHaveBeenCalledWith(
-    "The '%s' resolver returned `undefined` instead of a value. This is likely a bug in the resolver. Return `null` instead if you didn't mean to return a value.",
+    "The '%s' resolver returned `undefined` instead of a value. This is likely a bug in the resolver. If you didn't mean to return a value, use return `null` instead.",
     "Query.foo"
   );
 });