Warning: array_filter() [function.array-filter]: The first argument should be an array

Even if my variable $kwds was an array, and the function is_array returned true i don't know why it still threw a warning. To overpass it, instead of
$kwds=array_filter($kwds);
i wrote
$kwds=array_filter(array($kwds));
Now it works :) I Hope it will help somebody.