some progress

node_modules/mongoose/lib/helpers/path/flattenObjectWithDottedPaths.js

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+'use strict';
+
+const MongooseError = require('../../error/mongooseError');
+const isMongooseObject = require('../isMongooseObject');
+const setDottedPath = require('../path/setDottedPath');
+const util = require('util');
+
+/**
+ * Given an object that may contain dotted paths, flatten the paths out.
+ * For example: `flattenObjectWithDottedPaths({ a: { 'b.c': 42 } })` => `{ a: { b: { c: 42 } } }`
+ */
+
+module.exports = function flattenObjectWithDottedPaths(obj) {
+  if (obj == null || typeof obj !== 'object' || Array.isArray(obj)) {
+    return;
+  }
+  // Avoid Mongoose docs, like docs and maps, because these may cause infinite recursion
+  if (isMongooseObject(obj)) {
+    return;
+  }
+  const keys = Object.keys(obj);
+  for (const key of keys) {
+    const val = obj[key];
+    if (key.indexOf('.') !== -1) {
+      try {
+        delete obj[key];
+        setDottedPath(obj, key, val);
+      } catch (err) {
+        if (!(err instanceof TypeError)) {
+          throw err;
+        }
+        throw new MongooseError(`Conflicting dotted paths when setting document path, key: "${key}", value: ${util.inspect(val)}`);
+      }
+      continue;
+    }
+
+    flattenObjectWithDottedPaths(obj[key]);
+  }
+};