Fix crash using empty string for parametrized value more than once

Fixes #11563.

testing/python/metafunc.py

@@ -626,6 +626,13 @@ class TestMetafunc:
             ).make_unique_parameterset_ids()
             assert result == [expected]
 
+    def test_idmaker_duplicated_empty_str(self) -> None:
+        """Regression test for empty strings parametrized more than once (#11563)."""
+        result = IdMaker(
+            ("a",), [pytest.param(""), pytest.param("")], None, None, None, None, None
+        ).make_unique_parameterset_ids()
+        assert result == ["0", "1"]
+
     def test_parametrize_ids_exception(self, pytester: Pytester) -> None:
         """
         :param pytester: the instance of Pytester class, a temporary