I would agree, that looks pretty simple and fits your example.
But your example seems to be a special case, since a string containing a space is not strictly 'empty' as far as PHP is concerned. So even if there was a PHP function to perform this action, I would guess it would fail.
Likewise, 'empty' values includes '0' and empty array's which would cause your current test to fail.
Just encountered this again... an alternative... if you want to check that an array contains only empty values (that is PHP's definition of empty [uk.php.net]) then you could use array_filter() [uk.php.net], omitting the 2nd (callback) argument. The default behaviour is to filter out empty elements. So, this becomes...