The following assertion error is being seen with hopper.
I think the check is possibly bogus.

java.lang.AssertionError
        at java.nio.channels.spi.AbstractSelectableChannel.removeKey(AbstractSelectableChannel.java:118)
        at java.nio.channels.spi.AbstractSelector.deregister(AbstractSelector.java:169)
        at sun.nio.ch.DevPollSelectorImpl.implDereg(DevPollSelectorImpl.java:162)
        at sun.nio.ch.SelectorImpl.processDeregisterQueue(SelectorImpl.java:119)
        at sun.nio.ch.DevPollSelectorImpl.doSelect(DevPollSelectorImpl.java:65)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:62)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:67)
        at HttpServer$Server.run(HttpServer.java:66)