def getfixturedefs(
        self, argname: str, node: nodes.Node
    ) -> Sequence[FixtureDef[Any]] | None:
        """Get FixtureDefs for a fixture name which are applicable
        to a given node.

        Returns None if there are no fixtures at all defined with the given
        name. (This is different from the case in which there are fixtures
        with the given name, but none applicable to the node. In this case,
        an empty result is returned).

        :param argname: Name of the fixture to search for.
        :param node: The requesting Node.
        """
        try:
            fixturedefs = self._arg2fixturedefs[argname]
        except KeyError:
            return None
        return tuple(self._matchfactories(fixturedefs, node))
Get FixtureDefs for a fixture name which are applicable
        to a given node.

        Returns None if there are no fixtures at all defined with the given
        name. (This is different from the case in which there are fixtures
        with the given name, but none applicable to the node. In this case,
        an empty result is returned).

        :param argname: Name of the fixture to search for.
        :param node: The requesting Node.
        
src/_pytest/fixtures.py