Java 25.0.3 (Ubuntu). Also reproduces on Java 21 — the JDK only changes the exception message, not the type: on 21 it is argument type mismatch, on 25 it wraps an unboxing NPE (see the trace below).
Swing is a cross-platform user-interface toolkit to build desktop applications with Java and is packaged with the Java SDK. Build a user interface with different look-and-feels for any platform ...
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