PHP USort gives null warning when array is empty -

    function sort_multi_array($array, $key) {   if (is_null($array)) return 0;   $keys = array();   ($i=1;$i<func_num_args();$i++) {     $keys[$i-1] = func_get_arg($i);   }    // create custom search function pass usort   $func = function ($a, $b) use ($keys) {     ($i=0;$i<count($keys);$i++) {       if ($a[$keys[$i]] != $b[$keys[$i]]) {         return ($a[$keys[$i]] > $b[$keys[$i]]) ? -1 : 1;       }     }     return 0;   };    usort($array, $func);    return $array; } 

i'm building simple search query when reaches end i.e. no more entries in warning: usort() expects parameter 1 array, null given in

how can test see if array empty , return null result before reaches usort line?

thank you!

check before using usort if $array null or not.

if ($array !== null) {     usort($array, $func); }