fix(template): preserve non-string prefix elements in _replace_system

[he-yufeng]

_replace_system is responsible for building the no-system variant of prefix by replacing the {{SYSTEM}} placeholder in string elements. The current implementation uses a filter comprehension:

# before
return [p.replace('{{SYSTEM}}', '') for p in prefix if isinstance(p, str)]

The if isinstance(p, str) clause silently drops every non-string element. Token-ID lists like ['bos_token_id'] are legitimate prefix components — templates such as ziya, bluelm, and emu3_chat (and others in baai.py) use prefix=[['bos_token_id'], '{{SYSTEM}}']. When _replace_system runs (i.e. no system message is provided), the BOS token-ID entry disappears from meta.prefix, so every training and inference sequence for these templates starts without the expected leading token.

Fix: change the filter to a conditional expression so non-strings pass through unchanged:

# after
return [p.replace('{{SYSTEM}}', '') if isinstance(p, str) else p for p in prefix]

Adds a focused unit test in tests/general/test_template_meta.py that instantiates a TemplateMeta with a mixed prefix and asserts the list element survives __post_init__.

[gemini-code-assist]

Code Review

This pull request fixes a bug in _replace_system where non-string elements (such as list placeholders like ['bos_token_id']) were being filtered out from the template prefix. The method now correctly preserves non-string elements while stripping the {{SYSTEM}} placeholder from string elements. A corresponding unit test has been added to verify this behavior. I have no further feedback to provide.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[Jintao-Huang]

thanks!

[Jintao-Huang]

Please pass the lint checks:

pip install pre-commit
pre-commit run --all-files