ExceptionInInitializerError: Caused by: java.lang.NullPointerException

[JulyDev]

Hi:
When I run DroidUPnP app on xiaomi pad,sometimes it will crash:

03-13 13:49:08.089: E/AndroidRuntime(4360): FATAL EXCEPTION: cling-3
03-13 13:49:08.089: E/AndroidRuntime(4360): Process: org.droidupnp, PID: 4360
03-13 13:49:08.089: E/AndroidRuntime(4360): java.lang.ExceptionInInitializerError
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:711)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:64)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:95)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.server.Server.doStart(Server.java:282)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:64)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.fourthline.cling.transport.impl.jetty.JettyServletContainer.startIfNotRunning(JettyServletContainer.java:141)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.fourthline.cling.transport.impl.AsyncServletStreamServerImpl.run(AsyncServletStreamServerImpl.java:92)
03-13 13:49:08.089: E/AndroidRuntime(4360): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
03-13 13:49:08.089: E/AndroidRuntime(4360): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
03-13 13:49:08.089: E/AndroidRuntime(4360): at java.lang.Thread.run(Thread.java:841)
03-13 13:49:08.089: E/AndroidRuntime(4360): Caused by: java.lang.NullPointerException
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.util.StringUtil.asciiToLowerCase(StringUtil.java:106)
03-13 13:49:08.089: E/AndroidRuntime(4360): at org.eclipse.jetty.http.MimeTypes.(MimeTypes.java:138)
03-13 13:49:08.089: E/AndroidRuntime(4360): ... 10 more

What can be done to fix this problem ?Thanks for your help.