When users don't explicitly set `maxOutputTokens` in Google/Gemini endpoint
settings, LibreChat was sending `"maxOutputTokens": ""` instead of omitting
the field. This caused issues with Gemini SDK and AI reverse proxies that
expect numeric types.
Changes:
- Add `removeEmptyStrings=true` to `removeNullishValues()` in googleSchema
- Add `removeEmptyStrings=true` to `removeNullishValues()` in compactGoogleSchema
- Add `removeEmptyStrings=true` to `removeNullishValues()` in getGoogleConfig()
- Create comprehensive test suite for Google endpoint (45 tests)
The fix ensures empty strings for numeric fields like maxOutputTokens,
temperature, topP, and topK are properly removed from the request payload.
Closes#11187
