fix: WilcoBundleFinder.find() returns empty string instead of None, breaks Django finders.find()

[hartym]

Bug

WilcoBundleFinder.find(path, all=False) returns "" (empty string) when no file matches. This breaks Django's staticfiles.finders.find() aggregation.

Root cause

In wilco/bridges/django/finders.py, lines 55 and 69:

return [] if all else ""

Django's finders.find() iterates all finders and collects results:

for finder in get_finders():
    result = finder.find(path, all=all)
    if not all and result:
        return result
    if not isinstance(result, (list, tuple)):
        result = [result]
    matches.extend(result)
if matches:
    return matches
return [] if all else None

When all=False, the "" is falsy so it doesn't trigger early return. But then it gets wrapped into [""] and added to matches. Since [""] is truthy, finders.find() returns [""] instead of None.

Impact

Any middleware or tool that calls finders.find() receives [""] (a list) instead of None for non-wilco paths. For example, whitenoise 6.x calls finders.find() and then passes the result to os.path.exists(), which raises:

TypeError: stat: path should be string, bytes, os.PathLike or integer, not list

This only manifests when a static file is not found by any other finder (e.g. a hashed filename in development mode).

Suggested fix

Return None instead of "" when all=False:

# finders.py, line 55 and 69
return [] if all else None

This matches the convention used by Django's built-in finders (FileSystemFinder, AppDirectoriesFinder) which return the empty matches list for no-match with all=False, or a string path on match.

[hartym]

The fix in 0.5.2 (None instead of "") is still broken. Django's finders.find() wraps non-list results into [None], which is truthy, so it's returned as a match.

Django's built-in finders (FileSystemFinder, AppDirectoriesFinder) both return [] for no-match, regardless of the all parameter. The fix should match that convention:

return []

Not None, not "", just [] in all no-match branches.