# Buggy code
def slice_graph(graph, node, frontier, include_frontier=False):
    """
    Generate a slice of the graph from the head node to the given frontier.

    :param networkx.DiGraph graph: The graph to work on.
    :param node: The starting node in the graph.
    :param frontier: A list of frontier nodes.
    :param bool include_frontier: Whether the frontier nodes are included in the slice or not.
    :return: A subgraph.
    :rtype: networkx.DiGraph
    """

    subgraph = networkx.DiGraph()

    for frontier_node in frontier:
        for simple_path in networkx.all_simple_paths(graph, node, frontier_node):
            for src, dst in zip(simple_path, simple_path[1:]):
                if include_frontier or (src not in frontier and dst not in frontier):
                    subgraph.add_edge(src, dst)

    return subgraph


# Traceback (TypeError)
Traceback (most recent call last):
File "$HOME/angr-dev/angr-management/angrmanagement/ui/widgets/qfunction_table.py", line 227, in _on_function_selected
self._selection_callback(selected_func)
File "$HOME/angr-dev/angr-management/angrmanagement/ui/views/functions_view.py", line 41, in _on_function_selected
self.workspace.on_function_selected(function)
File "$HOME/angr-dev/angr-management/angrmanagement/ui/workspace.py", line 57, in on_function_selected
self.views_by_category['disassembly'][0].display_function(function)
File "$HOME/angr-dev/angr-management/angrmanagement/ui/views/disassembly_view.py", line 171, in display_function
self._display_function(function)
File "$HOME/angr-dev/angr-management/angrmanagement/ui/views/disassembly_view.py", line 343, in _display_function
vr = self.workspace.instance.project.analyses.VariableRecoveryFast(the_func)
File "$HOME/angr-dev/angr/angr/analyses/analysis.py", line 108, in __call__
oself.__init__(*args, **kwargs)
File "$HOME/angr-dev/angr/angr/analyses/variable_recovery/variable_recovery_fast.py", line 510, in __init__
self._analyze()
File "$HOME/angr-dev/angr/angr/analyses/forward_analysis.py", line 557, in _analyze
self._analysis_core_graph()
File "$HOME/angr-dev/angr/angr/analyses/forward_analysis.py", line 583, in _analysis_core_graph
self._add_input_state(n, output_state)
File "$HOME/angr-dev/angr/angr/analyses/forward_analysis.py", line 605, in _add_input_state
self._state_map[succ] = self._merge_states(succ, *([ self._state_map[succ], input_state ]))
File "$HOME/angr-dev/angr/angr/analyses/variable_recovery/variable_recovery_fast.py", line 551, in _merge_states
return states[0].merge(states[1], successor=node.addr)
File "$HOME/angr-dev/angr/angr/analyses/variable_recovery/variable_recovery_fast.py", line 448, in merge
processor_state=self.processor_state.copy().merge(other.processor_state),
File "$HOME/angr-dev/angr/angr/analyses/variable_recovery/variable_recovery_fast.py", line 53, in merge
self.bp = max(self.bp, other.bp)
TypeError: '>' not supported between instances of 'NoneType' and 'NoneType'

# Fixed code
def slice_graph(graph, node, frontier, include_frontier=False):
    """
    Generate a slice of the graph from the head node to the given frontier.

    :param networkx.DiGraph graph: The graph to work on.
    :param node: The starting node in the graph.
    :param frontier: A list of frontier nodes.
    :param bool include_frontier: Whether the frontier nodes are included in the slice or not.
    :return: A subgraph.
    :rtype: networkx.DiGraph
    """

    subgraph = networkx.DiGraph()

    for frontier_node in frontier:
        for simple_path in networkx.all_simple_paths(graph, node, frontier_node):
            for src, dst in zip(simple_path, simple_path[1:]):
                if include_frontier or (src not in frontier and dst not in frontier):
                    subgraph.add_edge(src, dst)
    if not list(subgraph.nodes):
        # HACK: FIXME: for infinite loop nodes, this would return an empty set, so we include the loop body itself
        # Make sure this makes sense (EDG thinks it does)
        if (node, node) in graph.edges:
            subgraph.add_edge(node, node)
    return subgraph