some progress

node_modules/mongoose/lib/helpers/isSimpleValidator.js

@@ -0,0 +1,22 @@
+'use strict';
+
+/**
+ * Determines if `arg` is a flat object.
+ *
+ * @param {Object|Array|String|Function|RegExp|any} arg
+ * @api private
+ * @return {Boolean}
+ */
+
+module.exports = function isSimpleValidator(obj) {
+  const keys = Object.keys(obj);
+  let result = true;
+  for (let i = 0, len = keys.length; i < len; ++i) {
+    if (typeof obj[keys[i]] === 'object' && obj[keys[i]] !== null) {
+      result = false;
+      break;
+    }
+  }
+
+  return result;
+};