[omrzk]

When an HTTP proxy authenticates a username with an empty password, Proxy.from_url("http://login:@proxy:port") silently omits Proxy-Authorization and the proxy rejects CONNECT with 407. The HTTP BasicAuth encoder already supports that credential pair, but the request builder tests the password's truthiness before using it.

Treat an explicitly empty password as configured when the username is present. Add a request-header regression and controls for ordinary passwords, absent passwords, and anonymous connections.

Validation on Python 3.12.3/Linux, using the repository's locked development dependencies:

• The new empty-password case fails on unchanged master; four controls pass.
• A local TCP proxy fixture receives no credentials and returns 407 on unchanged master; the patched public Proxy.from_url() path authenticates and exchanges tunnel bytes.
• All 395 sync/async and v1/v2 tests pass, with 94% package coverage.
• Full Ruff lint/format checks and Mypy (78 files) pass; git diff --check passes.

The TCP reproduction uses a local proxy fixture, without an external proxy service.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.36%. Comparing base (b3259cf) to head (9e2778d).
⚠️ Report is 2 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #50      +/-   ##
==========================================
+ Coverage   94.30%   94.36%   +0.06%     
==========================================
  Files          55       55              
  Lines        1562     1562              
==========================================
+ Hits         1473     1474       +1     
+ Misses         89       88       -1     

Flag	Coverage Δ
unit	94.36% <100.00%> (+0.06%)	⬆️

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