fix: case of undefined

Author: cesco69

packages/pg/lib/utils.js

@@ -45,7 +45,7 @@ function arrayString(val) {
 // note: you can override this function to provide your own conversion mechanism
 // for complex types, etc...
 var prepareValue = function (val, seen) {
-  if (typeof val === 'object') {
+  if (typeof val === 'object' || typeof val === 'undefined') {
     // null and undefined are both null for postgres
     if (val == null) {
       return null