BaseSession.java

   @Override
   public void setAttribute(String name, Object value) {
      synchronized (this){
         Object attribute = getAttribute(name);
         if(!Objects.equal(value, attribute) ){
            super.setAttribute(name, value);
            dirty = true;
         }
      }
   }

   @Override
   public void removeAttribute(String name) {
      synchronized (this){
         Object attribute = getAttribute(name);
         if(attribute != null){
            super.removeAttribute(name);
            dirty = true;
         }
      }
   }