mybatis if test 不为空字符串或null

<sql id="public_content"> 
  	<if test="productId != null and productId !=''" > 
        and  a.product_id = #{productId,jdbcType=VARCHAR} 
      </if> 
      <if test="productDefinId != null" > 
        and a.product_defin_id = #{productDefinId,jdbcType=VARCHAR} 
      </if> 
      <if test="productUid != null and productUid !=''"> 
        and a.product_uid = #{productUid,jdbcType=VARCHAR} 
      </if> 
      <if test="productKey != null" > 
        and a.product_key = #{productKey,jdbcType=VARCHAR} 
      </if> 
      <if test="prouuctSecret != null" > 
        and a.prouuct_secret = #{prouuctSecret,jdbcType=VARCHAR} 
      </if> 
      <if test="productPass != null" > 
        and a.product_pass = #{productPass,jdbcType=VARCHAR} 
      </if> 
      <if test="productVisitPass != null" > 
        and a.product_visit_pass = #{productVisitPass,jdbcType=VARCHAR} 
      </if> 
      <if test="createTime != null and createTime !=''" > 
        and a.create_time = #{createTime,jdbcType=VARCHAR} 
      </if> 
      <if test="pageSize != null and pageNum !=null " >       
         ORDER BY a.product_id DESC limit #{pageNum},#{pageSize} 
      </if> 
  </sql>