[Bug]--database parameters are not specified,When you dynamically monitor a new table, a null database is created

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/incubator-doris/issues?q=is%3Aissue) and found no similar issues.

### Version

flink1.15.2
flink-doris-connector-1.15-25.1.0.jar

### What's Wrong?

not specified --database
but --single-sink true
Create a new table in the upstream source database，The logs are as follows：

INFO org.apache.doris.flink.sink.schema.SchemaChangeManager [] - Execute SQL: CREATE TABLE IF NOT EXISTS `null`.`t_test`(`id` BIGINT COMMENT '' ) UNIQUE KEY(`id`) DISTRIBUTED BY HASH(`id`) BUCKETS AUTO PROPERTIES ('replication_num'='1','light_schema_change'='true')
INFO org.apache.doris.flink.sink.writer.serializer.jsondebezium.JsonDebeziumSchemaChangeImplV2 [] - create table ddl status: true, add tableMapping live_test.t_test,null.t_test

### What You Expected?

Dynamically added tables are written to the corresponding downstream databases

### How to Reproduce?

not specified --database
but --single-sink true
Create a new table in the upstream source database

### Anything Else?

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

Reproduce the case with --single-sink true and no --database while creating a new upstream table, then inspect the logged SQL from SchemaChangeManager and the table mapping reported by JsonDebeziumSchemaChangeImplV2. Done means dynamically added tables are created in their corresponding downstream databases rather than a database named null.

Written by the indexing model from the issue text.