fix(schema): treat creating dotted path with no parent as creating a …

…nested path

Fix #9020

lib/schema.js

@@ -656,21 +656,24 @@ Schema.prototype.path = function(path, obj) {
   const subpaths = path.split(/\./);
   const last = subpaths.pop();
   let branch = this.tree;
+  let fullPath = '';
 
-  subpaths.forEach(function(sub, i) {
+  for (const sub of subpaths) {
+    fullPath = fullPath += (fullPath.length > 0 ? '.' : '') + sub;
     if (!branch[sub]) {
+      this.nested[fullPath] = true;
       branch[sub] = {};
     }
     if (typeof branch[sub] !== 'object') {
       const msg = 'Cannot set nested path `' + path + '`. '
           + 'Parent path `'
-          + subpaths.slice(0, i).concat([sub]).join('.')
+          + fullPath
           + '` already set to type ' + branch[sub].name
           + '.';
       throw new Error(msg);
     }
     branch = branch[sub];
-  });
+  }
 
   branch[last] = utils.clone(obj);