# Buggy code
def _sort_category_hierarchy(self):
    """Sort category hierarchy."""
    # First create a hierarchy of TreeNodes
    self.category_hierarchy_lookup = {}

    def create_hierarchy(cat_hierarchy, parent=None):
        """Create category hierarchy."""
        result = []
        for name, children in cat_hierarchy.items():
            node = utils.TreeNode(name, parent)
            node.children = create_hierarchy(children, node)
            node.category_path = [pn.name for pn in node.get_path()]
            node.category_name = self.category_path_to_category_name(node.category_path)
            self.category_hierarchy_lookup[node.category_name] = node
            if node.category_name not in self.config.get("HIDDEN_CATEGORIES"):
                result.append(node)
        return natsort.natsorted(
            result, key=lambda e: e.name, alg=natsort.ns.F | natsort.ns.IC
        )

    root_list = create_hierarchy(self.category_hierarchy)
    # Next, flatten the hierarchy
    self.category_hierarchy = utils.flatten_tree_structure(root_list)


# Traceback (KeyError)
########################################
TaskError - taskid:render_galleries:output/galleries/index.html
PythonAction Error
Traceback (most recent call last):
File "/home/kwpolska/virtualenvs/nikola-py2/lib/python2.7/site-packages/doit/action.py", line 360, in execute
returned_value = self.py_callable(*self.args, **kwargs)
File "/home/kwpolska/git/nikola/nikola/plugins/task/galleries.py", line 466, in render_gallery_index
self.site.render_template(template_name, output_name, context)
File "/home/kwpolska/git/nikola/scripts/../nikola/nikola.py", line 607, in render_template
template_name, None, local_context)
File "/home/kwpolska/git/nikola/nikola/plugins/template/mako.py", line 88, in render_template
data = template.render_unicode(**context)
File "/home/kwpolska/virtualenvs/nikola-py2/lib/python2.7/site-packages/mako/template.py", line 452, in render_unicode
as_unicode=True)
File "/home/kwpolska/virtualenvs/nikola-py2/lib/python2.7/site-packages/mako/runtime.py", line 807, in _render
**_kwargs_for_callable(callable_, data))
File "/home/kwpolska/virtualenvs/nikola-py2/lib/python2.7/site-packages/mako/runtime.py", line 839, in _render_context
_exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
File "/home/kwpolska/virtualenvs/nikola-py2/lib/python2.7/site-packages/mako/runtime.py", line 865, in _exec_template
callable_(context, *args, **kwargs)
File "/home/kwpolska/Desktop/nikola-translated-path/cache/.mako.tmp/base.tmpl.py", line 91, in render_body
__M_writer(unicode(base.meta_translations()))
File "/home/kwpolska/Desktop/nikola-translated-path/cache/.mako.tmp/base_helper.tmpl.py", line 274, in render_meta_translations
__M_writer(unicode(_link(permalink, None, langname)))
File "/home/kwpolska/git/nikola/scripts/../nikola/nikola.py", line 765, in link
return self.path(*args, is_link=True)
File "/home/kwpolska/git/nikola/scripts/../nikola/nikola.py", line 729, in path
path = self.path_handlers[kind](name, lang)
KeyError: u'/galleries/galleries/index.html'

# Fixed code
def _sort_category_hierarchy(self):
    """Sort category hierarchy."""
    # First create a hierarchy of TreeNodes
    self.category_hierarchy_lookup = {}

    def create_hierarchy(cat_hierarchy, parent=None):
        """Create category hierarchy."""
        result = []
        for name, children in cat_hierarchy.items():
            node = hierarchy_utils.TreeNode(name, parent)
            node.children = create_hierarchy(children, node)
            node.category_path = [pn.name for pn in node.get_path()]
            node.category_name = self.category_path_to_category_name(node.category_path)
            self.category_hierarchy_lookup[node.category_name] = node
            if node.category_name not in self.config.get("HIDDEN_CATEGORIES"):
                result.append(node)
        return natsort.natsorted(
            result, key=lambda e: e.name, alg=natsort.ns.F | natsort.ns.IC
        )

    root_list = create_hierarchy(self.category_hierarchy)
    # Next, flatten the hierarchy
    self.category_hierarchy = hierarchy_utils.flatten_tree_structure(root_list)