fix STRING_SESSION environment variable setting invalid

[jiesou]

Description

Please carefully read the Contributing note and Code of conduct before making any pull requests. And, Do not make a pull request to merge into master unless it is a hotfix. Use the development branch instead.

Issues fixed by this PR

Type of changes

• [x] Bug fix
• [ ] New feature
• [ ] Enhancement
• [ ] Documentation

Checklist:

• [x] My code follows the style guidelines of this project
• [x] My pull request is unique and no other pull requests have been opened for these changes
• [x] I have read the Contributing note and Code of conduct
• [x] I am responsible for any copyright issues with my code if it occurs in the future.

[omg-xtao]

@jiesou 请对 development 分支发起 pr