There is a possible issue in the KeepAlive Clearner implementation where a KeepAliveStream has been quite correctly queued for cleanup, while another thread reads off the remainder of the response body and closes the stream. Now when the cleaner thread comes along the HttpClient reference has been set to null as it is either closed or in the cache.

This does not happen often and the window for this to happen is quite small.

Exception in thread "Keep-Alive-SocketCleaner" java.lang.NullPointerException
at sun.net.www.http.KeepAliveStreamCleaner.run(KeepAliveStreamCleaner.java:89)
at java.lang.Thread.run(Thread.java:619)