Merge branch 'vkarpov15/Automatticgh-12844' of github.com:Automattic/mongoose into vkarpov15/Automatticgh-12844

Author: vkarpov15

lib/schemaType.js

@@ -463,7 +463,7 @@ SchemaType.prototype.index = function(options) {
  * will still throw MongoDB's default `E11000 duplicate key error` message.
  *
  * @param {Boolean} value
- * @param {String} message
+ * @param {String} [message]
  * @return {SchemaType} this
  * @api public
  */

types/index.d.ts

@@ -309,7 +309,7 @@ declare module 'mongoose' {
     eachPath(fn: (path: string, type: SchemaType) => void): this;
 
     /** Defines an index (most likely compound) for this schema. */
-    index(fields: IndexDefinition, options?: Omit<IndexOptions, 'unique'> & { unique?: boolean | undefined | [true, string] }): this;
+    index(fields: IndexDefinition, options?: Omit<IndexOptions, 'unique'> & { unique?: boolean | [true, string] }): this;
 
     /**
      * Define a search index for this schema.