diff --git a/chat2db-server/chat2db-plugins/chat2db-mysql/src/main/java/ai/chat2db/plugin/mysql/value/MysqlValueProcessor.java b/chat2db-server/chat2db-plugins/chat2db-mysql/src/main/java/ai/chat2db/plugin/mysql/value/MysqlValueProcessor.java
index 5aadec81..dbd9ddd7 100644
--- a/chat2db-server/chat2db-plugins/chat2db-mysql/src/main/java/ai/chat2db/plugin/mysql/value/MysqlValueProcessor.java
+++ b/chat2db-server/chat2db-plugins/chat2db-mysql/src/main/java/ai/chat2db/plugin/mysql/value/MysqlValueProcessor.java
@@ -22,7 +22,7 @@ public class MysqlValueProcessor extends DefaultSQLValueProcessor {
     public String getSqlValueString(ResultSet rs, int index) throws SQLException {
         Object obj = rs.getObject(index);
         if (obj == null) {
-            return null;
+            return "NULL";
         }
         String columnTypeName = rs.getMetaData().getColumnTypeName(index);
         if (MysqlColumnTypeEnum.GEOMETRY.name().equalsIgnoreCase(columnTypeName)