code: function UpdateDocumentRequest(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 an UpdateDocumentRequest.
  @memberof google.firestore.v1
  @interface IUpdateDocumentRequest
  @property {google.firestore.v1.IDocument|null} [document] UpdateDocumentRequest document
  @property {google.firestore.v1.IDocumentMask|null} [updateMask] UpdateDocumentRequest updateMask
  @property {google.firestore.v1.IDocumentMask|null} [mask] UpdateDocumentRequest mask
  @property {google.firestore.v1.IPrecondition|null} [currentDocument] UpdateDocumentRequest currentDocument
   
  Constructs a new UpdateDocumentRequest.
  @memberof google.firestore.v1
  @classdesc Represents an UpdateDocumentRequest.
  @implements IUpdateDocumentRequest
  @constructor
  @param {google.firestore.v1.IUpdateDocumentRequest=} [properties] Properties to set