code: function getLastListener(method_definition, emitter, callback) {
    if (emitter instanceof Function) {
      callback = emitter;
      callback = function() {};
    }
    if (!(callback instanceof Function)) {
      callback = function() {};
    }
    if (!((emitter instanceof EventEmitter) &&
         (callback instanceof Function))) {
      throw new Error('Argument mismatch in getLastListener');
    }
    var method_type = common.getMethodType(method_definition);
    var generator = listenerGenerators[method_type];
    return generator(method_definition, emitter, callback);
  }
docs: Creates the last listener in an interceptor stack.
  @param {grpc~MethodDefinition} method_definition
  @param {EventEmitter} emitter
  @param {function=} callback
  @return {grpc~Listener}