code: def get_kgXref_hg19(self):
          
          if self._kgXref_hg19 is None:
              self._kgXref_hg19 = self._load_kgXref(self._get_path_kgXref_hg19())
  
          return self._kgXref_hg19
docs: Get UCSC kgXref table for Build 37.
  
          Returns
          -------
          pandas.DataFrame
              kgXref table if loading was successful, else None