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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 _merge_meta_data(cls, first: "HistogramBase", second: "HistogramBase") -> dict: """Merge meta data of two histograms leaving only the equal values. (Used in addition and subtraction) """

        keys = set(first._meta_data.keys())
        keys = keys.union(set(second._meta_data.keys()))
        return {key:
                (first._meta_data.get(key, None) if first._meta_data.get(key, None) == second._meta_data.get(key, None) else None)
                for key in keys}