code: function _getLastInterceptor(method_definition, channel, responder) {
    var callback = (responder instanceof Function) ? responder : function() {};
    var emitter = (responder instanceof EventEmitter) ? responder :
                                                        new EventEmitter();
    var method_type = common.getMethodType(method_definition);
    var generator = interceptorGenerators[method_type];
    return generator(method_definition, channel, emitter, callback);
  }
docs: Creates the last interceptor in an interceptor stack.
  @private
  @param {grpc~MethodDefinition} method_definition
  @param {grpc.Channel} channel
  @param {function|EventEmitter} responder
  @return {Interceptor}