[Bug]

### 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

doris ,1.2.4
flink ,1.1.4
flink-doris-connect , 1.1.1

### What's Wrong?

flink写doris，报错：Reason: column(xxx) values is null while columns is not nullable

UNIQUE 模型。xxx字段列 ：NOT NULL DEFAULT '1' 。已经指定了not null后的默认值。

当插入的字段值为null，为何不生效默认值？而是直接报错了。

### What You Expected?

当插入的字段值为null，为何不生效默认值？而是直接报错了。
期望： 不报错，且not null后指定的默认值生效。

### How to Reproduce?

_No response_

### Anything Else?

_No response_

### Are you willing to submit PR?

- [X] 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)

Start with the Flink Doris connector 1.1.1 and the reported Doris 1.2.4 setup, focusing on the path that handles a null value for a NOT NULL column with a default. Reproduce the failure with a UNIQUE model and the provided column definition; done means the insert no longer errors and the configured default is applied.

Written by the indexing model from the issue text.