$sum = [0, 0, 0, 0];

echo count($sum) / array_sum($sum);
// Warning: Division by zero

$arraySum = 0.00001 + array_sum($sum);
$number = count($sum) / $arraySum;
echo round($number, 2);
// Result is 0;

Just add some small number to the one you are not sure that it will be bigger than zero.
Easy as that.