fix: Nullable Primitives

[Piszmog]

When a java primitive is nullable, call setNull and do not try to pass a nullable parameter into a non-nullable JDBC method.

Fixes: #31

Details

• Added a field called PrimitiveType to ktType
• Added a function called ktPrimitiveType to return the primitive types (as found in java.sql.Types)
• When creating the set method, if it is null and is a primitive type, perform a null check on the arugment

Appendix

• Add examples of nullable primitives Piszmog/sqlc-gen-kotlin#4