The patch moved all test code to EDT from the main thread, now the listRepaint field is used on both threads without synchronization. The test also started to use invokeLater which is not necessarily executed before the next sleep ends.

java.lang.NullPointerException
at java.base/java.util.Objects.requireNonNull(Objects.java:220)
at ListRepaint.main(ListRepaint.java:45)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:573)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1575)