Find any valid target for "ref()" in the graph by its name and
        package name, or None for any package.

def find_refable_by_name(self, name, package):
        """Find any valid target for "ref()" in the graph by its name and
        package name, or None for any package.
        """
        return self._find_by_name(name, package, 'nodes', NodeType.refable())