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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read_neighbor_graph_pickle(gname, graph_dir):
 """Read in neighbor graph for given gene. Parameters gname : str name of gene graph_dir : str directory containing gene graphs Returns ------- gene_graph : dict or None neighbor graph as dict for gene. Returns None if not found. """

    graph_path = os.path.join(graph_dir, gname+".pickle")
    if os.path.exists(graph_path):
        with open(graph_path) as handle:
            gene_graph = pickle.load(handle)
        return gene_graph
    else:
        return None