From 90f15090423d6fa3ef0ad4395956b9e0a37fbd96 Mon Sep 17 00:00:00 2001
From: Muneeb Sheikh <muneikh@gmail.com>
Date: Sun, 11 Oct 2026 13:14:42 -0400
Subject: [PATCH] Preserve blank values when extending queries

---
 src/rfc3986/builder.py |  4 +++-
 tests/test_builder.py  | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/rfc3986/builder.py b/src/rfc3986/builder.py
index f8f19aa..d731198 100644
--- a/src/rfc3986/builder.py
+++ b/src/rfc3986/builder.py
@@ -325,7 +325,9 @@ def extend_query_with(self, query_items: _QueryType) -> "URIBuilder":
             URIBuilder(scheme=None, userinfo=None, host=None, port=None,
                     path=None, query='a=b+c&a=b+c', fragment=None)
         """
-        original_query_items = parse_qsl(self.query or "")
+        original_query_items = parse_qsl(
+            self.query or "", keep_blank_values=True
+        )
         if not isinstance(query_items, list):
             query_items = list(query_items.items())
 
diff --git a/tests/test_builder.py b/tests/test_builder.py
index eae3ec3..44efb6e 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -323,3 +323,19 @@ def test_geturl():
         "sigmavirus24/rfc3986"
     )
     assert expected == uri
+
+
+@pytest.mark.parametrize(
+    "original, expected",
+    [
+        ("a=", "a=&new=value"),
+        ("a=&a=1", "a=&a=1&new=value"),
+        ("flag&b=", "flag=&b=&new=value"),
+    ],
+)
+def test_extend_query_preserves_existing_blank_values(original, expected):
+    """Extending a query retains empty values and repeated parameters."""
+    original_builder = builder.URIBuilder(query=original)
+    extended = original_builder.extend_query_with({"new": "value"})
+    assert extended.query == expected
+    assert original_builder.query == original