ArgumentNullException is called when trying to stop streaming data

[minwater2]

I am currently streaming the user data using this

void SingleUserStream(object sender, ValueChangedEventArgs e)
_singleUserReference.ValueChanged += SingleUserStream;

and when I try to stop the stream using
_singleUserReference.ValueChanged -= SingleUserStream;
I get an

ArgumentNullException: Value cannot be null.
Parameter name: _unity_self
FirebaseREST.DatabaseReference.OnStopListening (UnityEngine.Networking.UnityWebRequestAsyncOperation obj) 
(at Assets/FirebaseREST/Database/DatabaseReference.cs:119)
FirebaseREST.DatabaseReference+<>c__DisplayClass28_1.<BeginListeningServerEvents>b__2 (UnityEngine.AsyncOperation ao) (at Assets/FirebaseREST/Database/DatabaseReference.cs:81)
UnityEngine.AsyncOperation.InvokeCompletionEvent () (at <a979f18d51af41179d12b797e8c5be14>:0)