ServiceExtensionResponse.result(String result)

Creates a successful response to a service protocol extension RPC.

Requires result to be a JSON object encoded as a string. When forming the JSON-RPC message result will be inlined directly.

Source 

ServiceExtensionResponse.result(String result)
    : _result = result,
      _errorCode = null,
      _errorDetail = null {
  if (_result is! String) {
    throw new ArgumentError.value(_result, "result", "Must be a String");
  }
}