Check an array for all null values

Here is a simple function to check an array to see if it contains all null values.

function allNulls($arr) {
    if(is_array($arr) && count(array_diff($arr, array(null))) == 0) {
            return true;
    }

    return false;
}

echo (allNulls(array(null,null,null)) ? "true" : "false") . PHP_EOL;
echo (allNulls(array(null,1,null)) ? "true" : "false") . PHP_EOL;
echo (allNulls(array("test",null,null)) ? "true" : "false") . PHP_EOL;
echo (allNulls(array("",null,null)) ? "true" : "false") . PHP_EOL;
echo (allNulls(array(0,null,null)) ? "true" : "false") . PHP_EOL;