请教高人空指针错误

Question

下面是相关代码
@Override
    public boolean onContextItemSelected(MenuItem item)throws IndexOutOfBoundsException{
        AdapterContextMenuInfo itemInfo = (AdapterContextMenuInfo) item.getMenuInfo(); //获取菜单信息
switch(item.getItemId()){
        case 1:
            int pos = (int)getListAdapter().getItemId(itemInfo.position);//此行报空指针错
            list.remove(pos);        
            adapter.notifyDataSetChanged();  
            DBAdapter dbAdapter = new DBAdapter(NoteActivity.this);
            dbAdapter.deleteOneData(pos);
       checkNull();
            Toast.makeText(getApplicationContext(), "已删除此记事", Toast.LENGTH_SHORT).show();  
            break;  
        case 2:
         Intent intent = new Intent(NoteActivity.this,EditActivity.class);
startActivity(intent);
        }
        return super.onContextItemSelected(item);
    }
 public List<Map<String, String>> getContent(){
     List<Map<String, String>>list = new ArrayList<Map<String,String>>();
     Map<String,String>map = new HashMap<String, String>();
     DBAdapter dbAdapter = new DBAdapter(NoteActivity.this);
     dbAdapter.open();
     Note[] content = dbAdapter.getAllData();
     if(content!=null){
     for(int i=0;i<content.length;i++){
     map = new HashMap<String, String>();
     map.put("num", "NO."+String.valueOf(i+1));
     map.put("title", content[i].title);
     list.add(map);
     }
     }
     if(!list.isEmpty()){
     return list;
     }else {
return null;
}
    }
public void listAdapter(){
     adapter= new SimpleAdapter(this,getContent(),R.layout.list,new String[]{"num","title"},new int[]{R.id.num,R.id.title});
listView.setAdapter(adapter);
        registerForContextMenu(getListView());//注册，使listview上的选项都作为一个菜单    }
请问这个空指针错误是怎么回事，该如何解决？谢谢大家了！