fix: check for err.constructor

Author: titanism

index.js

@@ -136,7 +136,7 @@ function errorHandler(
       err.message === 'Connection is closed.' ||
       err.name === 'RedisError' ||
       err.name === 'MaxRetriesPerRequestError' ||
-      Object.getPrototypeOf(err.constructor).name === 'RedisError'
+      (err.constructor && Object.getPrototypeOf(err.constructor).name === 'RedisError')
     ) {
       // redis errors (e.g. ioredis' MaxRetriesPerRequestError)
       err.status = 408;