android - RoboGuice injection -

i using code in android app (roboguice library):

@singleton public class usersessionprovider {     private user user;     @inject    private injector injector;     public synchronized user createsession() {       this.user = injector.getinstance(user.class);       return this.user;    }     public synchronized user getuser() {       return user;    }     public synchronized void destroysession() {       this.user = null;    }     public synchronized boolean issessionalive() {       return getuser() != null;    } } 

sometimes build gets bugged up, , application fails inject instance of injector in provider. when clean app , rebuild again works ok (for time). using gradle build chain , android studio. know how can stop happening?