[theman6660]

Normalizing an empty-path relative reference changes its rooted flag, so resolving it against a base URL can discard the base path. For example, normalizing ?x=1 before clicking it from http://example.com/a/b resolves to http://example.com/?x=1 instead of http://example.com/a/b?x=1.

Only add the empty-path slash when a host is present. Regression tests cover empty, query-only, fragment-only, and combined references through URL and DecodedURL; existing absolute-host slash normalization remains covered.

Validation on Windows / Python 3.12:

• Both new regression tests failed before the fix; 89 URL/DecodedURL tests pass afterward.
• Tests and module doctests: 134 passed, 3 deselected. The excluded hostname-strategy tests fail Hypothesis filtering health checks on pristine upstream 978f2e6 as well (see Tests are failing due to hypothesis filtering #186). The full suite is not claimed green.
• Black 21.7b0 on changed files and git diff --check pass. Older interpreter matrix not run.

Found during source inspection. Implementation, tests, and this description were prepared with OpenAI Codex at my request.