I want to set up the following:

public DataSet ExecuteQuery(string sCommand, string sTableName, SqlParameter[] aParams)
{
    return ExecuteQuery(sCommand, sTableName, aParams, null);
}
public DataSet ExecuteQuery(string sCommand, string sTableName, SqlParameter[] aParams, CommandType Type)
{
.
.
.
    if (Type == null)
    {
        Type = CommandType.Text;
    }
    oCommand.CommandType = Type;

}

This doesn't compile because I can't pass null to the last param, and I can't check in the IF to see if the param is null. What's the right way to do this?