fix(schema): retain _id: false in schema after nesting in another s…

…chema

Fix #8274

lib/schema.js

@@ -402,7 +402,6 @@ Schema.prototype.add = function add(obj, prefix) {
   // the `_id` option. This behavior never worked before 5.4.11 but numerous
   // codebases use it (see gh-7516, gh-7512).
   if (obj._id === false && prefix == null) {
-    delete obj._id;
     this.options._id = false;
   }
 
@@ -417,6 +416,10 @@ Schema.prototype.add = function add(obj, prefix) {
       throw new TypeError('Invalid value for schema path `' + fullPath +
         '`, got value "' + obj[key] + '"');
     }
+    // Retain `_id: false` but don't set it as a path, re: gh-8274.
+    if (key === '_id' && obj[key] === false) {
+      continue;
+    }
 
     if (Array.isArray(obj[key]) && obj[key].length === 1 && obj[key][0] == null) {
       throw new TypeError('Invalid value for schema Array path `' + fullPath +