Exception has occurred.

[mdino]

socket.onConnect((_) {
  print('Connected to server');
  socket.emit('joinGame', {'playerId': playerId, 'balance': balance, 'cpu': cpu, 'host': host,  'playerName': playerName,  'avatar': avatar});
});

Exception has occurred. DartError: NoSuchMethodError: 'toJSON' method not found Receiver: Instance of 'IdentityMap<String, Object>' Arguments: []

Why I always got exception on any socket.emit.. I try to Map it, json encode, decode (client and server side) everything and I always got the same error in visual studio.