close method
Closes the client and cleans up any resources associated with it.
It's important to close each client when it's done being used; failing to do so can cause the Dart process to hang.
Once close is called, no other methods should be called. If close is called while other asynchronous methods are running, the behavior is undefined.
Implementation
@override
void close() => super.noSuchMethod(Invocation.method(#close, []),
returnValueForMissingStub: null);