some progress

node_modules/mongoose/lib/error/parallelSave.js

@@ -0,0 +1,30 @@
+'use strict';
+
+/*!
+ * Module dependencies.
+ */
+
+const MongooseError = require('./');
+
+class ParallelSaveError extends MongooseError {
+  /**
+   * ParallelSave Error constructor.
+   *
+   * @param {Document} doc
+   * @api private
+   */
+  constructor(doc) {
+    const msg = 'Can\'t save() the same doc multiple times in parallel. Document: ';
+    super(msg + doc._id);
+  }
+}
+
+Object.defineProperty(ParallelSaveError.prototype, 'name', {
+  value: 'ParallelSaveError'
+});
+
+/*!
+ * exports
+ */
+
+module.exports = ParallelSaveError;