demerphq,
I stand by my claim. If the value before or after is undefined, then it is not desired. You need to keep moving forward until you find a key with a defined value.

Cheers - L~R

Update: After discussing this in the CB, I wanted to record why I interpreted next key with defined value versus just next key. It was based off of:

without going through all the trouble of making a for loop to check each element after '2' until find one defined.