c# - WCF unhandled exception by user code -

i'm developing wcf service c# , .net framework 4.0.

i have following code:

public long createuser(string username) {     try     {         if ((username == null) ||             (username.equals(string.empty)))             throw new argumentnullexception();          ...      }     catch (exception ex)     {         resultcode = 3;         throw ex;     }      ...  } 

when username == string.empty debugger stops , dialog said:

argumentnullexception unhandled user code. 

how can fix that?

update

want notify client there error in server side.

you need handle exception when using createuser method:

try {     myclass.createuser (user);  } catch (argumentnullexception ex) {  }