Merge pull request #836 from ditkachuk/fix-get-entity-fcm

 Fix getEntityFCMToken resolve and update README

README.md

@@ -455,6 +455,22 @@ class App extends Component {
             .catch(error => {
               //Error while deleting instance id
             });
+
+        // Use this functions instead of FCM.getFCMToken if you want revokes access of token
+        FCM.getEntityFCMToken()
+            .then(token => {
+              // Returns a token that authorizes an FCM Entity by Instance ID
+              // Store fcm token in your server
+            })
+        FCM.deleteEntityFCMToken()
+            .then( () => {
+              // Deleted token successfully
+              // Revokes access to a scope (action) for an entity previously authorized by getToken() with Instance ID
+              // This will reset token
+            })
+            .catch(error => {
+              // Error while deleting token
+            });
     }
 }
 ```

ios/RNFIRMessaging.m

@@ -408,6 +408,7 @@ RCT_EXPORT_METHOD(getEntityFCMToken:(RCTPromiseResolveBlock)resolve rejecter:(RC
 
     if (deviceToken == nil) {
         resolve(nil);
+        return;
     }
 
     [[FIRInstanceID instanceID]tokenWithAuthorizedEntity:entity scope:kFIRInstanceIDScopeFirebaseMessaging options:@{@"apns_token": deviceToken} handler:^(NSString * _Nullable token, NSError * _Nullable error) {