The implication is that ignoring MaxDirectMemorySize doesn't work out
of the box in Java 9+ now. However, you can make it work by setting
JVM flags to allow access to the new Cleaner class. Or set
MaxDirectMemorySize if it's an issue. Or do nothing if you don't
actually run up against the MaxDirectMemorySize limit, which seems to
default to equal the size of the JVM heap.