AttributeError: ‘NoneType‘ object has no attribute ‘author‘（Django操作數據庫時）

django操作數據庫時報錯Traceback (most recent call last): File 「E:/DjangoProject/test4_orm/app01/tests.py」, line 152, in book_obj.author.add(author_obj1,author_obj2) AttributeError: ‘NoneType’ object has no at

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