[Bug]: handle None server_version_info in get_isolation_level to prevent TypeError

[xxsc0529]

Describe the bug

handle None server_version_info in get_isolation_level to prevent TypeError

Environment

handle None server_version_info in get_isolation_level to prevent TypeError

Fast reproduce steps

handle None server_version_info in get_isolation_level to prevent TypeError

Expected behavior

No response

Actual behavior

No response

Additional context

No response