Fix bugs in agent api and update api document (#3996)
### What problem does this PR solve?
Fix bugs in agent api and update api document
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
api http return error when content is not found
- [x] Bug Fix (non-breaking change which fixes an issue)
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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
liuhua
Kevin Hu
so95