Get abstract states for all predecessors of the node, merge them, and return the merged state.

        :param node: The node in graph.
        :return:     A merged state, or None if no predecessor is available.

def _merge_state_from_predecessors(self, node):
        """
        Get abstract states for all predecessors of the node, merge them, and return the merged state.

        :param node: The node in graph.
        :return:     A merged state, or None if no predecessor is available.
        """

        preds = self._graph_visitor.predecessors(node)

        states = [ self._state_map[n] for n in preds if n in self._state_map ]

        if not states:
            return None

        return reduce(lambda s0, s1: self._merge_states(node, s0, s1), states[1:], states[0])