mybatis 3.4.6，日期字段做比较操作，日期字段为空时，报错

2018-04-06 18:04:26,614  INFO [OrderRelationController.java:345] : nested exception is org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: java.lang.IllegalArgumentException: invalid comparison: java.util.Date and java.lang.String
### Cause: java.lang.IllegalArgumentException: invalid comparison: java.util.Date and java.lang.String
2018-04-06 18:04:26,815 ERROR [MIBaseController.java:69] : 调用search接口。返回结果：{"body":{},"head":{"appVersion":"","dataVersion":"","deployVersion":"","msgCount":"","rspCode":"1","rspMsg":"查询失败"}}

  <sql id="condition_sql">
    	<if test="startTime !=null and startTime !='' "> and ordertime >= #{startTime} </if>
    	<if test="endTime !=null and endTime !='' "> and ordertime <=#{endTime} </if>
  </sql>

正确的配置如下：

  <sql id="condition_sql">
    	<if test="startTime !=null"> and ordertime >= #{startTime} </if>
    	<if test="endTime !=null"> and ordertime <=#{endTime} </if>
  </sql>