SQL Error Doesn't Stop Execution

I have some code that I inherited that I'm having an issue with.  It includes a class for database functionality.  At one point a call to a function, snippet below, results in a SQL error ('can't insert NULL into column MyColumn).  What is amazing and frustrating me is that it just Blows Right by the Error!  I thought it would raise the alarm bells, "hey!  I got a sql error."  I only see the error if I step through the code and look at the Exception that's caught.  I tried removing the catch statement entirely, thinking that would at least cause an unhandled exception error, but no go. 

How do I raise a big red flag to the user when SQL errors happen?  And how could it not be doing that automatically?  This is for an intranet site so I really don't care if they see ugly errors or not.

try
{
   sqlcommand = new SqlCommand();
   sqlcommand.Connection = DBInterface.DBConnection;
   sqlcommand.CommandText = strSQL;
   sqlcommand.CommandType = CommandType.Text;
   nRowsAffected = sqlcommand.ExecuteNonQuery();
}
catch (Exception ex)
{
   return -1;
}