问RoboGuice提供错误

EN

 public class FacebookAccessTokenProvider implements Provider<AccessToken>{
    @Inject FBAccountDao dao;

    public AccessToken get() 
    {
       List<FacebookAccount> accounts = null;

       dao.open();
       accounts = dao.findAll();
       dao.close();
       if (accounts != null && !accounts.isEmpty())
       {
          FacebookAccount account = accounts.get(0);
          return new AccessToken(account.getToken(), account.getExpires());
       }
      return null;
    }
 }

public class FacebookProvider implements Provider<Facebook>{

@Inject private AccessToken accessToken;

public Facebook get() 
{   

    if (accessToken != null)
    {
        Facebook facebook = new FacebookFactory().getInstance();
        facebook.setOAuthAppId(AppCredentials.FACEBOOK_APP_ID,AppCredentials.FACEBOOK_APP_SECRET);
        facebook.setOAuthPermissions(AppCredentials.FACEBOOK_PERMISSION);
        facebook.setOAuthAccessToken(accessToken);

        return facebook;
    }
    return null;
}

}

    public void configure(Binder binder) 
{
    binder.bind(FBAccountDao.class).toProvider(FBAccountDaoProvider.class);
    binder.bind(TwitterAccountDao.class).toProvider(TwitterAccountDaoProvider.class);
    binder.bind(TwitterFriendDao.class).toProvider(TwitterFriendDaoProvider.class);
    binder.bind(FeedDao.class).toProvider(FeedDaoProvider.class);
    binder.bind(Facebook.class).toProvider(FacebookProvider.class);
    binder.bind(Token.class).toProvider(TwitterAccessTokenProvider.class);
    binder.bind(Twitter.class).toProvider(TwitterProvider.class);
    binder.bind(AccessToken.class).toProvider(FacebookAccessTokenProvider.class);
}

java.lang.RuntimeException: Unable to start service com.soulfeed.service.FeedService@422368d8 with Intent { cmp=com.soulfeed/.service.FeedService (has extras) }: com.google.inject.ProvisionException: Guice provision errors:

1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34)
 but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable
while locating com.soulfeed.module.FacebookAccessTokenProvider
while locating facebook4j.auth.AccessToken
for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source)
while locating com.soulfeed.module.FacebookProvider
while locating facebook4j.Facebook

1 error
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2553)
at android.app.ActivityThread.access$2000(ActivityThread.java:134)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4867)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
at dalvik.system.NativeStart.main(Native Method)
Caused by: com.google.inject.ProvisionException: Guice provision errors:

 1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34)
 but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable
while locating com.soulfeed.module.FacebookAccessTokenProvider
while locating facebook4j.auth.AccessToken
for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source)
while locating com.soulfeed.module.FacebookProvider
while locating facebook4j.Facebook

1 error
at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987)
at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013)
at roboguice.inject.ContextScopedRoboInjector.getInstance(ContextScopedRoboInjector.java:143)
at com.soulfeed.request.AsyncRequestTask.<init>(AsyncRequestTask.java:64)
at com.soulfeed.request.FeedAsyncTask.<init>(FeedAsyncTask.java:33)
at com.soulfeed.service.FeedService.onStartCommand(FeedService.java:57)
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2536)
... 10 more
com.google.inject.ProvisionException: Guice provision errors:

1) null returned by binding at com.soulfeed.module.RoboGuiceModule.configure(RoboGuiceModule.java:34)
 but com.soulfeed.module.FacebookProvider.accessToken is not @Nullable
 while locating com.soulfeed.module.FacebookAccessTokenProvider
 while locating facebook4j.auth.AccessToken
 for field at com.soulfeed.module.FacebookProvider.accessToken(Unknown Source)
 while locating com.soulfeed.module.FacebookProvider
 while locating facebook4j.Facebook

1 error
at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987)
at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013)
at roboguice.inject.ContextScopedRoboInjector.getInstance(ContextScopedRoboInjector.java:143)
at com.soulfeed.request.AsyncRequestTask.<init>(AsyncRequestTask.java:64)
at com.soulfeed.request.FeedAsyncTask.<init>(FeedAsyncTask.java:33)
at com.soulfeed.service.FeedService.onStartCommand(FeedService.java:57)
at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2536)
at android.app.ActivityThread.access$2000(ActivityThread.java:134)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4867)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
at dalvik.system.NativeStart.main(Native Method)