Getting error when connecting to backend

[steve-cahn]

When I try connecting my flutter app, I get the following error:

_TypeError (type 'Null' is not a subtype of type 'int')

Here's my code:

IO.Socket? _socket;
_socket = IO.io('${Constants.wsUrl}',
        IO.OptionBuilder().enableForceNew().setTransports(['websocket']).setQuery({'token': token, 'payload': json.encode(payload)}).build());