Record.Builder api work with primitive types :

withInt(String, int)

As a result, a call builder.withInt("field", null) will compile but throw a NPE.

it would be better to have

withInt(String, Integer)

Then, a call builder.with("field", null) will store a null.

And, for non null value, int is boxed in Integer to be store on a Map .. So, result would be same.