往book对象set值时报NullPointerException，怎么处理呢？

if(bookChild.getName().equals("name")){

bookEntity.setName(bookChild.getStringValue());

}

else if(bookChild.getName().equals("author")){

bookEntity.setAuthor(bookChild.getStringValue());

}

else if(bookChild.getName().equals("year")){

bookEntity.setYear(bookChild.getStringValue());

}

else if(bookChild.getName().equals("price")){

bookEntity.setPrice(bookChild.getStringValue());

}

else if(bookChild.getName().equals("language")){

bookEntity.setLanguage(bookChild.getStringValue());

}