code: function Document(properties) {
                      this.fields = {};
                      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 Document.
  @memberof google.firestore.v1
  @interface IDocument
  @property {string|null} [name] Document name
  @property {Object.<string,google.firestore.v1.IValue>|null} [fields] Document fields
  @property {google.protobuf.ITimestamp|null} [createTime] Document createTime
  @property {google.protobuf.ITimestamp|null} [updateTime] Document updateTime
   
  Constructs a new Document.
  @memberof google.firestore.v1
  @classdesc Represents a Document.
  @implements IDocument
  @constructor
  @param {google.firestore.v1.IDocument=} [properties] Properties to set