JDBC native source produces non-null values for null values at the source

[yruslan]

Describe the bug

When an input schema has columns that map to Java primitive types (short, int, long), and JDBC Native is on, the resulting data contains default values (0) instead of nulls for nullable columns.

Code and/or configuration snippet that caused the issue

pramen.sources = [
  {
    name = "jdbc_source"
    factory.class = "za.co.absa.pramen.core.source.JdbcSource"

    jdbc = {
       ...
    }
    use.jdbc.native = true
  }
]

Expected behavior

Nullable fields should retain 'null' value when loaded via JDBC Native.

Context

• Pramen/pramen-py version: 1.9.9