function setDefaultOptions() {
    options = options || {};
    if (options.skipValidation == null) {
      options.skipValidation = false;
    }
  }
Build bulk write operations for `bulkSave()`.

@param {Array<Document>} documents The array of documents to build write operations of
@param {Object} options
@param {Boolean} options.skipValidation defaults to `false`, when set to true, building the write operations will bypass validating the documents.
@param {Boolean} options.timestamps defaults to `null`, when set to false, mongoose will not add/update timestamps to the documents.
@return {Array<Promise>} Returns a array of all Promises the function executes to be awaited.
@api private