`array_distinct` fails when getting null as list

[rluvaton]

Describe the bug

When having array_distinct on null, the query fails

To Reproduce

Run the following in datafusion-cli

select array_distinct(a) from values ([1, 2, 3]), ([1, 3, 1]), (null) as X(a);

Internal error: UDF returned a different number of rows than expected. Expected: 3, Got: 2.
This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker

Expected behavior

To not fail and return the correct result

Additional context

I'll create PR to fix this week