请教这段简单的读取list的action为什么报空指针

package Action;import java.util.Iterator;import java.util.List;import Manager.BookManager;import admin.Book;import com.opensymphony.xwork2.ActionSupport;@SuppressWarnings("serial")public class ActionDemo01 extends ActionSupport {    private BookManager bookmanager;//接收业务层 使用spring管理    private List<Book> list;//接收查询到的list    private String bname;//接受的name    @SuppressWarnings("unchecked")    @Override    public String execute() throws Exception {        // TODO Auto-generated method stub        Book book = new Book();        book.setBname(bname);        list = bookmanager.booklist();// 这行报空指针 list是这个方法的值 return                                        // hibernateTemplate.find("from Book");        bookmanager.addBook(book);        Iterator it = list.iterator();        while (it.hasNext()) {            System.out.println(it.next());        }        return "ser";    }    public BookManager getBookmanager() {        return bookmanager;    }    public void setBookmanager(BookManager bookmanager) {        this.bookmanager = bookmanager;    }    public List<Book> getList() {        return list;    }    public void setList(List<Book> list) {        this.list = list;    }    public String getBname() {        return bname;    }    public void setBname(String bname) {        this.bname = bname;    }}