adapter getView报空

@Override

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder viewHolder;
    if(convertView==null){
        viewHolder=new ViewHolder();
        convertView= LayoutInflater.from(context).inflate(R.layout.list_item,null);
        viewHolder.textView= (TextView) convertView.findViewById(R.id.text);
        convertView.setTag(viewHolder);
    }else {
        viewHolder= (ViewHolder) convertView.getTag();
    }
    viewHolder.textView.setText(list.get(position));
    return convertView;
}


java.lang.NullPointerException
        at android.view.LayoutInflater.from(LayoutInflater.java:211)
        at com.jxthelp.adapter.DrawerAdapter.getView(DrawerAdapter.java:48)
        
        
        48为：convertView= LayoutInflater.from(context).inflate(R.layout.list_item,null);
        
        为何会报空指针