public function where(string $field, $operator, $value = null)
{
if (is_null($value)) {
$value = $operator;
$operator = '=';
}

return $this->filter(function ($data) use ($field, $operator, $value) {
if (strpos($field, '.')) {
list($field, $relation) = explode('.', $field);

$result = $data[$field][$relation] ?? null;
} else {
$result = $data[$field] ?? null;
}