Create valid dict without root href

[gadomski]

Related issues:

• Closes Creating a collection without links has an unexpected side-effect #183

Description:

Catalogs and Collections always have a root href. If the root Catalog or Collection (e.g. itself) does not have a self href, the dictionary serialization included a root link with href set to null, which is invalid. This fix removes the root link if it doesn't have a valid href.

Not required for items because they don't have a root link by default.

I discovered this problem when trying to write-then-read a very simple Collection using save_object, but the problem proved to be in the dict serialization.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• [ ] Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[gadomski]

Whoops, my markdown linter added some spaces to the CHANGELOG. If those are unwanted noise I can remove, LMK. Cool, someone else's linter already hit these changes, disregard.

[codecov-commenter]

Codecov Report

Base: 94.37% // Head: 94.37% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (5ca4901) compared to base (e77cd0a).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #896   +/-   ##
=======================================
  Coverage   94.37%   94.37%           
=======================================
  Files          83       83           
  Lines       12015    12026   +11     
  Branches     1136     1137    +1     
=======================================
+ Hits        11339    11350   +11     
  Misses        496      496           
  Partials      180      180           

Impacted Files	Coverage Δ
pystac/catalog.py	91.58% <100.00%> (ø)
tests/test_catalog.py	99.02% <100.00%> (+<0.01%)	⬆️
tests/test_collection.py	99.61% <100.00%> (+0.01%)	⬆️

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[pjhartzell]

I think the changes address #183 from a practical standpoint. The creation of null href root links seems embedded in pystac (editing catalog.py such that a root link that will have a null href is not created causes multiple test failures).

[gadomski]

editing catalog.py such that a root link that will have a null href is not created causes multiple test failures

Yup, I found the same thing -- PySTAC kind of expects a root, whether it has a href or not.