Cannot test if required integer query parameter is empty

[duharound]

When having an endpoint like this

ENDPOINT("GET", "/ids", getId, QUERY(Int32, id))

it is not possible for me to check if the endpoint was called with an empty query parameter id, i.e. /ids?id=.
The problem is, that when the string to int32 conversion is performed like

bool success;
v_int32 number = oatpp::utils::conversion::strToInt32(oatpp::String(""), success);

the conversion of the empty string returns the number 0 and success is set to true. The reason is the comparison with the string length here. In the given example, this means that id would automatically default to 0. What should I do, if I would like to have a different default value?