mybatis查询报空指针异常java.lang.NullPointerException

操作失败，nested exception is org.apache.ibatis.exceptions.PersistenceException: 
\n### Error querying database.  
Cause: java.lang.NullPointerException\n### 
The error may exist in cn/com/icbf/operationanalysis/mapper/AccountCustomerDataAnalysisMapper.xml\n### The error may involve 
cn.com.icbf.operationanalysis.mapper.AccountCustomerDataAnalysisMapper.cbcAppointCaseAmount\n### 
The error occurred while handling results
\n### SQL: select sum(cbc_commission_amount) from         account_customer_data_analysis          WHERE customer= ?\n### Cause: java.lang.NullPointerException

这个时候查看一下sql查询出的数据是不是NULL，而实体的类型是不是不能为空
我这里的报错是我的字段类型是Bigdecimal而查出来的是null所以需要在sql加上判断：
IFNULL(sum(cbc_commission_amount),0)

select IFNULL(sum(cbc_commission_amount),0) fromaccount_customer_data_analysis

判断不为空就可以正常

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