Cannot set a frame with no defined index and a value that cannot be converted to a Series

• ValueError: Cannot set a frame with no defined index and a value that cannot be converted to a Series
• 不能設置沒有定義的索引的frame對象和沒有被轉換爲Series的值
• 錯誤代碼：

df['PREDICT'] = df.apply(self.__predict, axis=1)

• 錯誤原因：df對象是空值Empty DataFrame