FIX:
org.apache.ibatis.binding.BindingException: Mapper method 'com.alibaba.swork.info.common.mapper.QualityDataOfTeamMapper.getAvgIssueFixedDuration attempted to return null from a method with a primitive return type (double).
加上 ifnull 的语句：
select ifnull(round(avg(c.fixed_duration/3600/24),2),0) from issue c
