Getting NullPointerException in GWT app but not sure how -

getting uncaught exception escaped java.lang.nullpointerexception: null

i getting error when calling

private final observerregistrationimpl<events.wordlistevent> wordlistadditionobservers =  new observerregistrationimpl<events.wordlistevent>();  public void addwordlists(arraylist<wordlist> wordlists) {     for(wordlist wl : wordlists) {         gwt.log( "model: adding wordlist: "+wl.getname());         this.wordlists.add(wl);                     //error happens on line below         this.wordlistadditionobservers.notifyobservers(this, new events.wordlistevent(wl));      } } 

i checked in debug mode , saw wordlistadditionobservers, w1 , this objects. none null. wrong?

here observerregistrationimpl class

public class observerregistrationimpl<t> implements observable<t> {      private list<observer<t>> observers = new arraylist<observer<t>>();       @override     public void addobserver(observer<t> o) {         this.observers.add(o);     }      @override     public void removeallobservers() {         this.observers.clear();     }      @override     public void removeobserver(observer<t> o) {         this.observers.remove(o);     }      @override     public void notifyobservers(modelviewinterface model, t event) {         for(observer<t> o : this.observers)             o.notify(model, event);     }  } 

here stacktrace

uncaught exception escaped <pre>java.lang.nullpointerexception: null     @ com.example.gwt.myapplication.listeditor.client.observerregistrationimpl.notifyobservers(observerregistrationimpl.java:29)     @ com.example.gwt.myapplication.listeditor.client.model.addwordlists(model.java:103)     @ com.example.gwt.myapplication.listeditor.client.controllerauthentication$2.onxmlparsed(controllerauthentication.java:74)     @ com.example.gwt.myapplication.listeditor.client.controllerauthentication$2.onxmlparsed(controllerauthentication.java:1)     @ com.example.gwt.myapplication.listeditor.client.remoterequest.doparsexml(remoterequest.java:291)     @ com.example.gwt.myapplication.listeditor.client.remoterequest.access$0(remoterequest.java:282)     @ com.example.gwt.myapplication.listeditor.client.remoterequest$1.onresponsereceived(remoterequest.java:209)     @ com.google.gwt.http.client.request.fireonresponsereceived(request.java:287)     @ com.google.gwt.http.client.requestbuilder$1.onreadystatechange(requestbuilder.java:393)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(unknown source)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)     @ java.lang.reflect.method.invoke(unknown source)     @ com.google.gwt.dev.shell.methodadaptor.invoke(methodadaptor.java:103)     @ com.google.gwt.dev.shell.methoddispatch.invoke(methoddispatch.java:71)     @ com.google.gwt.dev.shell.oophmsessionhandler.invoke(oophmsessionhandler.java:157)     @ com.google.gwt.dev.shell.browserchannel.reacttomessageswhilewaitingforreturn(browserchannel.java:1714)     @ com.google.gwt.dev.shell.browserchannelserver.invokejavascript(browserchannelserver.java:165)     @ com.google.gwt.dev.shell.modulespaceoophm.doinvoke(modulespaceoophm.java:120)     @ com.google.gwt.dev.shell.modulespace.invokenative(modulespace.java:507)     @ com.google.gwt.dev.shell.modulespace.invokenativeobject(modulespace.java:264)     @ com.google.gwt.dev.shell.javascripthost.invokenativeobject(javascripthost.java:91)     @ com.google.gwt.core.client.impl.impl.apply(impl.java)     @ com.google.gwt.core.client.impl.impl.entry0(impl.java:188)     @ sun.reflect.generatedmethodaccessor14.invoke(unknown source)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)     @ java.lang.reflect.method.invoke(unknown source)     @ com.google.gwt.dev.shell.methodadaptor.invoke(methodadaptor.java:103)     @ com.google.gwt.dev.shell.methoddispatch.invoke(methoddispatch.java:71)     @ com.google.gwt.dev.shell.oophmsessionhandler.invoke(oophmsessionhandler.java:157)     @ com.google.gwt.dev.shell.browserchannel.reacttomessages(browserchannel.java:1669)     @ com.google.gwt.dev.shell.browserchannelserver.processconnection(browserchannelserver.java:401)     @ com.google.gwt.dev.shell.browserchannelserver.run(browserchannelserver.java:222)     @ java.lang.thread.run(unknown source)</pre> 

i followed problem in debugger , noticed thowing exception @ following gwt code

} catch (invocationtargetexception e) {   // if here, means exception being thrown   // java javascript   wrapexception(returnvalue, e.gettargetexception());   return true; 

(answered in comments. converted community wiki answer. see question no answers, issue solved in comments (or extended in chat) )

the op wrote:

it turns out view getting passed controller null because doing private controllerwordlists controller = new controllerwordlists(this); in instance variable. why possible? why there no compile error? weird.