def get_statistical_uncertainty_hist(hists):
    """
    Sum all histograms in hists and rename as stat.unc for statistical uncertainty overlay
    """

    if len(hists) == 0:
        return None
    statistical_uncertainty_hist = hists[0].Clone("stat.unc")
    for hist in hists[1:]:
        statistical_uncertainty_hist.Add(hist)
    return statistical_uncertainty_hist