点击侧边栏 item 的设置报空指针

if(fragment!=null){
            if(currentFragment==null || !currentFragment.getClass().getName().equals(fragment.getClass().getName()) )
            {
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,fragment)
                        .commit();
                currentFragment=fragment;
            }
        }

判断加个fragment!=null 非空判断防止空指针