This is a regression introduced by JDK-8048020 - which might happen in the uncommon case where: pattern is a simple name (not a full path), and the .lck file already exists on disk (and hasn't been created by another FileHandler in the same VM).
In that case, we will check whether we have write permission in the directory in which the lck file is present. The catch is that if the file name is a simple name (not composed), then Path.getParentPath() will return null, and Files.isWritable() will throw NPE.
Exception in thread "main" java.lang.NullPointerException
at java.nio.file.Files.provider(Files.java:96)
at java.nio.file.Files.isAccessible(Files.java:2454)
at java.nio.file.Files.isWritable(Files.java:2520)
at java.util.logging.FileHandler.openFiles(FileHandler.java:466)