Issue with expansion of null @value values.

[kasei]

Expand test t0019 seems to reveal an issue with the Expansion algorithm step 15.2:

If the value of result's @value entry is null, then set result to null.

I believe this needs to return null instead of just updating the value of result. This will prevent that null from being converted to an empty array in step 21.

[gkellogg]

@kasei good catch, moved it below the check for @json, and also check for empty array.

Please acknowledge.

[kasei]

@gkellogg looks good, thanks!