Compare 2 arrays. Replace the missing data of 1 array with default array

$array1 = array('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3');
$array2 = array('key2' => 'new_value2', 'key4' => 'value4');

foreach ($array2 as $key => $value) {
    if (!isset($array1[$key])) {
        $array1[$key] = $value;
    }
}

print_r($array1);