我这样写mybatis的条件查询有问题吗，为什么不能输入空的值进行查询

                SELECT tm.id,tm.merchants_name,tm.merchants_type,
      tu.name as username,dept.name as deptname,tm.status
      FROM t_merchants as tm,t_user as tu,department as dept
      WHERE tm.user_id=tu.id AND tu.department_id=dept.id

      <if test="merchants_name!=null and merchants_name!='' ">
            AND tm.merchants_name LIKE CONCAT('%',#{merchants_name},'%')
      </if>

      <if test="merchants_type!=null and merchants_type!='' ">
          AND tm.merchants_type =#{merchants_type}
      </if>

      <if test="user_id!=null and user_id!='' and user_id!=0 ">
          AND tm.user_id =#{user_id}
      </if>

      <if test="status!=null and status!='' ">

          AND tm.status =#{status}

      </if>

if语句在中包裹

 SELECT tm.id,tm.merchants_name,tm.merchants_type,
      tu.name as username,dept.name as deptname,tm.status
      FROM t_merchants as tm,t_user as tu,department as dept
    <  WHERE>
      <if test="merchants_name!=null and merchants_name!='' ">
            AND tm.merchants_name LIKE CONCAT('%',#{merchants_name},'%')
      </if>

      <if test="merchants_type!=null and merchants_type!='' ">
          AND tm.merchants_type =#{merchants_type}
      </if>

      <if test="user_id!=null and user_id!='' and user_id!=0 ">
          AND tm.user_id =#{user_id}
      </if>

      <if test="status!=null and status!='' ">

          AND tm.status =#{status}
                and tm.user_id=tu.id 
                AND tu.department_id=dept.id
< /WHERE>
      </if>

额粘贴错误了最后的if在｛#status｝后面