Support empty password when using local mysql for test

[zhangzhw8]

1. Support empty password with warning log when using local mysql for test
2. Fix some flake8 problem by the way.

[designcomputer]

@zhangzhw8 Thank you for your contribution! While the addition of support for empty passwords in local MySQL testing could be convenient, it raises some concerns:

1. Security Risks: Allowing empty passwords, even in a testing environment, could lead to accidental configurations being deployed in production, which poses a significant security vulnerability.
2. Best Practices: This change might encourage practices that deviate from secure coding standards, potentially impacting the reliability of the system.
3. Safeguards: It is unclear from the current implementation whether there are adequate safeguards to prevent this feature from being used outside of a testing context.

We are currently reviewing the potential risks versus the benefits of this change.