#54 null pointer error

[Crashfourit]

java.lang.NullPointerException
com.logicalloy.ale.plugin.device.thingmagic.ThingMagicMercury$Listener.tellReader(ThingMagicMercury.java:207)
com.logicalloy.ale.plugin.device.thingmagic.ThingMagicMercury$Listener.stop(ThingMagicMercury.java:193)
com.logicalloy.ale.plugin.device.thingmagic.ThingMagicMercury.stop(ThingMagicMercury.java:105)
com.logicalloy.ale.LogicalReader.removeDevice(LogicalReader.java:106)
com.logicalloy.ale.LogicalReader.removeDevice(LogicalReader.java:131)
com.logicalloy.ale.mgmt.DevicesAction.update(DevicesAction.java:154)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:270)
org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187)
org.apache.struts.actions.LookupDispatchAction.execute(LookupDispatchAction.java:150)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:616)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:428)
org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:830)
org.displaytag.filter.ResponseOverrideFilter.doFilter(ResponseOverrideFilter.java:125)
org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:471)
org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:568)
org.mortbay.http.HttpContext.handle(HttpContext.java:1530)
org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:633)
org.mortbay.http.HttpContext.handle(HttpContext.java:1482)
org.mortbay.http.HttpServer.service(HttpServer.java:909)
org.mortbay.http.HttpConnection.service(HttpConnection.java:820)
org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:986)
org.mortbay.http.HttpConnection.handle(HttpConnection.java:837)
org.mortbay.http.SocketListener.handleConnection(SocketListener.java:245)
org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)