providerID should be nil in additionalUserInfo for signInAnonymouslyWithCompletion: (#3452)

* Testing for additionalUserInfo when signing in anonymously

Author: collinjackson

Example/Auth/Tests/FIRAuthTests.m

@@ -1468,6 +1468,12 @@ - (void)testSignInAnonymouslySuccess {
     XCTAssertTrue([NSThread isMainThread]);
     [self assertUserAnonymous:result.user];
     XCTAssertNil(error);
+    FIRAdditionalUserInfo *userInfo = result.additionalUserInfo;
+    XCTAssertNotNil(userInfo);
+    XCTAssertTrue(userInfo.isNewUser);
+    XCTAssertNil(userInfo.username);
+    XCTAssertNil(userInfo.profile);
+    XCTAssertNil(userInfo.providerID);
     [expectation fulfill];
   }];
   [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];

Firebase/Auth/Source/Auth/FIRAuth.m

@@ -928,7 +928,7 @@ - (void)signInAnonymouslyWithCompletion:(nullable FIRAuthDataResultCallback)comp
           return;
         }
         FIRAdditionalUserInfo *additionalUserInfo =
-          [[FIRAdditionalUserInfo alloc] initWithProviderID:FIREmailAuthProviderID
+          [[FIRAdditionalUserInfo alloc] initWithProviderID:nil
                                                     profile:nil
                                                    username:nil
                                                   isNewUser:YES];