我想使用jdbc（使用mysql数据库）通过preparestatement将空值插入到datetime字段中。我尝试了以下方法，但没有任何效果。
我有一个方法“util.dateconvertdate”，它用来将输入日期转换为格式化的字符串类型

public static String dateconvertdate(Timestamp timestamp) {
            Date date=null;
            String formattedDate="";
            if(timestamp != null){
                SimpleDateFormat sdf = new SimpleDateFormat("dd-MMM-yyyy hh:mm:ss");
                SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
                 Date date1 = new java.util.Date(timestamp.getTime());
                 formattedDate = formatter.format(date1);
        }
            else return "NULL";

            return formattedDate;
        }

我用来检查它是否返回null或date

if(Util.dateconvertdate(rs.getTimestamp("fld_dob")) !=null){
                    pmystmt.setString(17, (Util.dateconvertdate(rs.getTimestamp("fld_dob"))));
} else{
 pmystmt.setNull(17, java.sql.Types.NULL);
}

我试着

pmystmt.setNull(17, java.sql.Types.DATE);

pmystmt.setNull(17, Types.NULL);

pmystmt.setInt(17, Types.NULL);

pmystmt.setString(17, "NULL");

pmystmt.setNull(17, Types.DATE);

pmystmt.setString(17, null);

pmystmt.setDate(17, null);

但什么都不起作用，就像抛出异常一样

com.mysql.jdbc.MysqlDataTruncation: Data truncation: Incorrect datetime value: 'NULL' for column 'dob' at row 1
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2936)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1601)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1710)
    at com.mysql.jdbc.Connection.execSQL(Connection.java:2436)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1402)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1694)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1608)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1593)
    at com.members.App_users.AddRecords(App_users.java:66)
    at com.main.Start.main(Start.java:47)

任何帮助都将不胜感激。谢谢