private function mapOperator($operator)
{
if (array_key_exists($operator, $this->shortOperators)) {
$operator = $this->shortOperators[$operator];
}
if (!in_array($operator, $this->allowedOperators)) {
throw new InvalidArgumentException(sprintf('Invalid operator `%s` given. Valid operators are %s.', $operator, implode(', ', $this->allowedOperators)));
}
return $operator;
}