[issue-4276]fix jdbc set value null bug

[Keven0Liu]

…4276

What is the purpose of the change

The singleton mode maintains long connections instead of using one connection for each sql

Related issues/PRs

Related issues: #4276
Related pr:#4277

Brief change log

• change oneline finaly log

Checklist

• I have read the Contributing Guidelines on pull requests.
• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the Linkis mailing list first)
• If this is a code change: I have written unit tests to fully verify the new behavior.

[peacewong]

Call the Close after the Execute method should be modified. You can refer to the implementation of Prestoec