Fix perfect match missed for headers with empty values

CHANGELOG.rst

@@ -13,6 +13,7 @@ dev
 
 - Support for Python 3.14 has been added.
 - Support for PyPy 3.11 has been added.
+- Fixed perfect match missed for headers with empty values
 
 
 **Bugfixes**

src/hpack/hpack.py

@@ -313,7 +313,7 @@ def add(self, to_add: tuple[bytes, bytes], sensitive: bool, huffman: bool = Fals
         # can use the indexed literal.
         index, name, perfect = match
 
-        if perfect:
+        if perfect is not None:
             # Indexed representation.
             encoded = self._encode_indexed(index)
         else:

tests/test_hpack.py

@@ -126,6 +126,18 @@ def test_indexed_header_field(self):
         assert e.encode(header_set, huffman=False) == result
         assert list(e.header_table.dynamic_entries) == []
 
+    def test_indexed_header_field_empty_value_string(self):
+        """
+        The header field representation uses an indexed header field, from
+        the static table.
+        """
+        e = Encoder()
+        header_set = {':authority': ''}
+        result = b'\x81'
+
+        assert e.encode(header_set, huffman=False) == result
+        assert list(e.header_table.dynamic_entries) == []
+
     def test_indexed_header_field_from_static_table(self):
         e = Encoder()
         e.header_table_size = 0