private function buildNotCondition($operator, $operands)
{
if (count($operands) != 1) {
throw new InvalidParamException("Operator '{$operator}' requires exactly one operand.");
}
$operand = reset($operands);
if (is_array($operand)) {
$operand = $this->buildCondition($operand);
}
return [$operator => $operand];
}