修复切换分类时，标签不清空的BUG

src/main/resources/mapper/ai/material/MaterialDao.xml

@@ -132,11 +132,13 @@
         user_id = #{user_id}
         <if test="category_id != null and category_id != ''">, category_id = #{category_id}</if>
         <if test="material_name != null and material_name != ''">, material_name = #{material_name}</if>
-        <if test="tag_ids != null and tag_ids != ''">, tag_ids = #{tag_ids}</if>
-        <if test="image_thumb_url != null and image_thumb_url != ''">, image_thumb_url = #{image_thumb_url}</if>
-        <if test="image_url != null and image_url != ''">, image_url = #{image_url}</if>
-        <if test="file_url != null and file_url != ''">, file_url = #{file_url}</if>
-        <if test="pan_baidu_url != null and pan_baidu_url != ''">, pan_baidu_url = #{pan_baidu_url}</if>
+        <!-- 允许为空 -->
+        <if test="tag_ids != null">, tag_ids = #{tag_ids}</if>
+        <if test="image_thumb_url != null">, image_thumb_url = #{image_thumb_url}</if>
+        <if test="image_url != null">, image_url = #{image_url}</if>
+        <if test="file_url != null">, file_url = #{file_url}</if>
+        <if test="pan_baidu_url != null">, pan_baidu_url = #{pan_baidu_url}</if>
+        <!-- -->
         <if test="is_copyright != null and is_copyright != ''">, is_copyright = #{is_copyright}</if>
         WHERE id = #{material_id}
     </update>