Fix by_name() raising TypeError instead of returning None when nothing matches

[keeltrace]

AI Fully Automated PR - Review With Care

Summary

by_name() on a KGObject subclass without a client (the local
instance-library path used by controlled terms) raised
TypeError: object of type 'NoneType' has no len() when the requested
name did not match any instance, instead of returning None.

Reproduction (fairgraph master at time of fix; no KG connection needed):

from fairgraph.openminds.v5.controlled_terms import Species
Species.by_name("definitely not a species")
# TypeError: object of type 'NoneType' has no len()

Root cause

In fairgraph/kgobject.py, the instance-library branch of by_name()
used _instance_lookup.get(name, None). When nothing matched, objects
was set to None, and the following if len(objects) == 0: check
dereferenced it. The "contains" branch already initialised an empty
list, so only exact matches were affected.

Fix

One line: default to an empty list — cls._instance_lookup.get(name, [])
— so the existing "no match → return None" path works as documented and
matches the behaviour of from_id() with an unknown id.

Tests

New offline regression test file test/test_by_name.py (no network or
KG credentials required), covering:

• no-match returns None (regression for this issue)
• match="contains" with no match returns None
• single match is returned
• multiple matches warn and return the first; all=True returns all
• invalid match value raises ValueError

Verified that the new test fails with the exact reported TypeError
when the one-line fix is reverted, and passes with it applied.
Full suite: 88 passed, 57 skipped (KG-connection tests), 0 failures.

Fixes #130

[keeltrace]

AI generated Maintainer review summary for Fairgraph PR #133. Summary reviewed and approved for posting by Keeltrace.

• Code fix is correct and merge-worthy. The one-line change from .get(name, None) to .get(name, []) cleanly fixes the crash and preserves existing API behavior.
• Tests are good. They cover the regression plus normal hit, contains, duplicate, all=True, and invalid-match behavior.
• No code changes requested. The implementation can be approved as-is.
• Upstream CI has not actually run yet. GitHub Actions is currently action_required, so a maintainer needs to authorize it before merge.
• Two PR-description corrections are advisable:
  • The reproduction says fairgraph 0.14.0 but uses a v5 import that does not exist in 0.14.0.
  • get_by_id() should likely say from_id().
• There is a separate pre-existing wording bug where the error says "exact" instead of "equals", but this PR should not be expanded to fix it.

Overall: approve after CI passes; only clean up the PR description.