code: public <T> Future<T> invoke(String methodName, Object argument, Class<T> returnType) {
  		return invoke(methodName, argument, returnType, new HashMap<String, String>());
  	}
docs: Invokes the given method with the given arguments and returns
  immediately. The {@code Future<T>} object that is returned can be used to
  retrieve the result.
  
  @param methodName the name of the method to invoke
  @param argument   the arguments to the method
  @param returnType the return type
  @param <T>        the return type
  @return the response {@code Future<T>}