array_filter Flag will ignored when callable is null

From manual page: https://php.net/function.array-filter

If the callback parameter is set to null, the flag is ignored. I expect array_filter to use an empty check for the mode used on key, or value, or both. But the flag is ignored and each time only the value is checked for empty.

Example:

array_filter([''=>'2',0=>'3',0,5=>3,null,'',[]], null, ARRAY_FILTER_USE_BOTH); does not filter the elements where key or value are empty. Only the elements where value is empty are filtered.

I expected all elements where key or value are empty to be filtered.

and

array_filter([''=>'2',0=>'3',0,5=>3,null,'',[]], null, ARRAY_FILTER_USE_KEY); does not filter the elements where key is empty. Only the elements where value is empty are filtered.

I had expected that all elements whose keys are empty would be filtered.

Start with the array_filter manual page linked in the report and compare its description of a null callback with the supplied ARRAY_FILTER_USE_BOTH and ARRAY_FILTER_USE_KEY examples. Done means the documentation clearly states the flag behavior and the expected handling of empty keys and values.