if(data.ColumnName == null)
{
    ...
}

if(data.ColumnName.HasValue)
{
    ...
}

if(data.ColumnName == 0 /* or 0x000? */)
{
    ...
}

if(data.GetColumnValue("Column Name") == null)
{
    ...
}

if(data.IsNull("ColumnName")) { ... }

SELECT isNull(columnName, 0) FROM TABLENAME...

Select isNUll(columnName, 'N/A') FROM TABLENAME ...