fix: Use ResultSet.getObject to respect nullable columns of the basic SQL data types

[ichizero]

Description

Use ResultSet.getObject for the generation code of sqlc-gen-kotlin to respect nullable columns of the basic SQL data types.

Fixes #20

Details

java.sql.ResultSet.get{SpecificType}, such as ResultSet.getInt, ResultSet.getBoolean, returns the zero value of each types when the selected value is SQL NULL.

"Returns: the column value; if the value is SQL NULL, the value returned is false."

https://docs.oracle.com/en/java/javase/21/docs/api/java.sql/java/sql/ResultSet.html#getBoolean(int)

On the other hand, ResultSet.getObject returns null when the selected value is SQL NULL.

https://docs.oracle.com/en/java/javase/21/docs/api/java.sql/java/sql/ResultSet.html#getObject(int,java.lang.Class)

Both pgjdbc/PgResultSet.getObject, mysql-connector-j/ResultSetImpl.getObject implements ResultSet.getObject with nullable column handling and basic SQL data types detection, so I think sqlc-gen-kotlin should be use it and rely on driver implementations.

Appendix

• fyi: Use ResultSet.getObject & Update examples ichizero/sqlc-gen-kotlin#1
  • Update examples with this PR