Merge pull request #14431 from Atharv-Bobde/patch-1

Added Null check in case schema.options['type'][0] is undefined

Author: vkarpov15

lib/document.js

@@ -1388,6 +1388,7 @@ Document.prototype.$set = function $set(path, val, type, options) {
     if (schema.options &&
         Array.isArray(schema.options[typeKey]) &&
         schema.options[typeKey].length &&
+        schema.options[typeKey][0] &&
         schema.options[typeKey][0].ref &&
         _isManuallyPopulatedArray(val, schema.options[typeKey][0].ref)) {
       popOpts = { [populateModelSymbol]: val[0].constructor };