Empty docstring results in "fixture not found"

[sed-i]

Describe the bug
I have a couple scenarios that reuse the same test methods.
In one of my "When"s, I attempt to pass an empty docstring.
As a result, pytest-bdd complains for that particular test that the docstring fixture does not exist.

file /home/aegis/.cache/uv/builds-v0/.tmpsi0712/lib/python3.12/site-packages/pytest_bdd/scenario.py, line 296
          def scenario_wrapper(request: FixtureRequest, _pytest_bdd_example: dict[str, str]) -> Any:
E       fixture 'docstring' not found
>       available fixtures: _pytest_bdd_example, abort_on_fail, anyio_backend, anyio_backend_name, anyio_backend_options, cache, capfd, capfdbinary, caplog, capsys, capsysbinary, context, doctest_namespace, event_loop, free_tcp_port, free_tcp_port_factory, free_udp_port, free_udp_port_factory, interface_tester, loki_charm, loki_container, monkeypatch, ops_test, pytestbdd_stepdef_given_rules, pytestbdd_stepdef_given_trace, pytestbdd_stepdef_then_modified rules match, pytestbdd_stepdef_then_trace, pytestbdd_stepdef_when_extra labels are injected, pytestbdd_stepdef_when_trace, pytestconfig, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory, unused_tcp_port, unused_tcp_port_factory, unused_udp_port, unused_udp_port_factory
>       use 'pytest --fixtures [testpath]' for help on them.

/home/aegis/.cache/uv/builds-v0/.tmpsi0712/lib/python3.12/site-packages/pytest_bdd/scenario.py:296

To Reproduce

  Scenario: Empty extra labels leaves rules unchanged
    Given rules
      """
      groups:
        - rules:
            - labels:
                severity: warning
                team: some-team
      """
    When extra labels are injected
      """
      """
    Then modified rules match
      """
      groups:
        - rules:
            - labels:
                severity: warning
                team: some-team
      """

@when("extra labels are injected", target_fixture="modified_rules")
def when_extra_labels_injected(docstring, rules):
    extra_labels = yaml.safe_load(docstring) or {}

    return "..."

Expected behavior
I expected the docstring fixture to contain the the empty string, "".

Additional context
As a workaround, I changed the docstring to

"""
+---
"""

Version

• pytest version: 8.3.5
• pytest-bdd version: 8.1.0
• OS: Ubuntu 26.04