code: function ListenResponse(properties) {
                      if (properties)
                          for (var keys = Object.keys(properties), i = 0; i < keys.length; ++i)
                              if (properties[keys[i]] != null)
                                  this[keys[i]] = properties[keys[i]];
                  }
docs: Properties of a ListenResponse.
  @memberof google.firestore.v1
  @interface IListenResponse
  @property {google.firestore.v1.ITargetChange|null} [targetChange] ListenResponse targetChange
  @property {google.firestore.v1.IDocumentChange|null} [documentChange] ListenResponse documentChange
  @property {google.firestore.v1.IDocumentDelete|null} [documentDelete] ListenResponse documentDelete
  @property {google.firestore.v1.IDocumentRemove|null} [documentRemove] ListenResponse documentRemove
  @property {google.firestore.v1.IExistenceFilter|null} [filter] ListenResponse filter
   
  Constructs a new ListenResponse.
  @memberof google.firestore.v1
  @classdesc Represents a ListenResponse.
  @implements IListenResponse
  @constructor
  @param {google.firestore.v1.IListenResponse=} [properties] Properties to set