\`assert \"string\"\` always passes in Python because non-empty strings
are truthy. This silently skips input validation:
- **variable_assigner.py line 51**: \`assert \"Variable is not
complete.\"\` → \`raise ValueError(\"Variable is not complete.\")\`
- **loop.py line 59**: \`assert \"Loop Variable is not complete.\"\` →
\`raise ValueError(\"Loop Variable is not complete.\")\`
Without this fix, incomplete variables pass validation silently and
cause a confusing KeyError on the next line.
### What problem does this PR solve?
issue:
https://github.com/infiniflow/ragflow/issues/10427
change:
new component variable assigner
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
