mybatis离谱bug乱转类型

字符串传入的参数被转成了int：

@Param("online") String online

			<if test="online == '0'">
				and (heart_time is null or heart_time <![CDATA[ < ]]> UNIX_TIMESTAMP(SUBDATE(now(),INTERVAL 8 MINUTE)) )
			</if>
			<if test="online == '1'">
				and heart_time is not null and heart_time >= UNIX_TIMESTAMP(SUBDATE(now(),INTERVAL 8 MINUTE))
			</if>

以上代码，既不进online == '0'也不进online == '1'，因为被mybatis转成了int类型。
需要这样判断：

			<if test="online == 0">
				and (heart_time is null or heart_time <![CDATA[ < ]]> UNIX_TIMESTAMP(SUBDATE(now(),INTERVAL 8 MINUTE)) )
			</if>
			<if test="online == 1">
				and heart_time is not null and heart_time >= UNIX_TIMESTAMP(SUBDATE(now(),INTERVAL 8 MINUTE))
			</if>