How do I test for and handle a return of null in the following code?

               try
               {
                   OleDbConnection connection = new
OleDbConnection(connectionString);
                   connection.Open();
                   OleDbCommand command = new OleDbCommand(SQL_Query,
connection);
                   scalarReturned =
command.ExecuteScalar().ToString();
                   command.Dispose();
                   connection.Close();
               }
               catch (Exception ex)
               {

               }

This is part of a data-handling class I'm building, and I use this
method for pulling single values from one of my lookup tables where
the structure is fixed. It works fine; however I want to be able to
handle when the query returns null...of course trying to convert null
ToString() generates an error.

I suppose I could just trap that error, but I'd rather design it so no
error is generated.

Thanks.