code: function WriteRequest(properties) {
                      this.writes = [];
                      this.labels = {};
                      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 WriteRequest.
  @memberof google.firestore.v1
  @interface IWriteRequest
  @property {string|null} [database] WriteRequest database
  @property {string|null} [streamId] WriteRequest streamId
  @property {Array.<google.firestore.v1.IWrite>|null} [writes] WriteRequest writes
  @property {Uint8Array|null} [streamToken] WriteRequest streamToken
  @property {Object.<string,string>|null} [labels] WriteRequest labels
   
  Constructs a new WriteRequest.
  @memberof google.firestore.v1
  @classdesc Represents a WriteRequest.
  @implements IWriteRequest
  @constructor
  @param {google.firestore.v1.IWriteRequest=} [properties] Properties to set