When JdbcItemReader is used with columnType property, we can't distinguish between actual null and default value on some column types such as Int.

For example, when we set columnTypes=Int as a property of JdbcItemReader, ResultSet#getInt() will be invoked, and it returns 0 both case SQL NULL and 0. in such case we need to invoke ResultSet#wasNull() to investigate whether the last column read had a value of SQL NULL.

Reproducer: https://github.com/lbtc-xxx/jberet-wasnull