教科書一般的使用，無奈遇到了莫名的錯誤，小白分不清是官方和新版As和gradle的沖突還是什么錯，求指導。
報錯如下：
org.litepal.exceptions.DataSupportException: Attempt to invoke virtual method 'java.lang.Class[] java.lang.reflect.Constructor.getParameterTypes()' on a null object reference

代碼如下：

 public void onClick(View v) {
    switch (v.getId()) {
        case R.id.create_database:
            database = LitePal.getDatabase();
            showTable();
            break;
        case R.id.save_data:
            Book book = new Book("think in java", "null", "￥100");
            book.save();
            showTable();
            break;
        default:
            break;
    }
}
void showTable() {
    List<Book> allBooks = DataSupport.findAll(Book.class);
    StringBuffer stringBuffer = new StringBuffer();
    for (int i = 0; i < allBooks.size(); i++) {
        stringBuffer.append("authorname:" + allBooks.get(i).getAuthorName() + "\n");
        stringBuffer.append("bookname:" + allBooks.get(i).getBookName() + "\n");
        stringBuffer.append("price:" + allBooks.get(i).getPrice() + "\n");
    }
    logText.setText(stringBuffer.toString());
}