code: void setError(Exception error) {
  		if (this.error != null) {
  			throw new IllegalStateException(
  					"Cannot reassign the error value of a response.");
  		}
  		this.error = error;
  		this.ready = true;
  		synchronized (this) {
  			this.notifyAll();
  		}
  	}
docs: Sets the exception for this response and notifies any waiting threads.
  Any calls to get() will have the exception thrown when an Exception is
  set.
  
  @param error
  the exception for this response.