Boy Scout rule
You may know the boy scout rule:
Always leave the campground cleaner than you found it!
So, when there is some litter: pick it up.
Boy Scout rule in Clean Code
Always leave the code you are editing a little bit better than you found it
- If there is no documentation, write some minimal top level docu.
- If there is no gitignore file, add one.
- If the dependencies are not locked, you do it.
- If there are no tests, add at least one.
There is always something even a junior developer can do.
Further reading
10 tips for creating co-ownership in a code base
Writing as a complementary skill for your SW engineering career
