Some methods on java.net.http.HttpRequest.Builder, like the POST(), PUT() and method() accept a BodyPublisher. These methods throw a NullPointerException when the given BodyPublisher is null. The default implementation of the HttpRequest.Builder in the JDK throws a NullPointerException of the form:

Exception in thread "main" java.lang.NullPointerException
  at java.base/java.util.Objects.requireNonNull(Objects.java:220)
  at java.net.http/jdk.internal.net.http.HttpRequestBuilderImpl.POST(HttpRequestBuilderImpl.java:180)

It would be good to include what is null in the exception message of that NullPointerException.

This was brought up in the net-dev mailing list discussion https://mail.openjdk.org/pipermail/net-dev/2025-November/028733.html