code: def make_canonical_identifier(self,id):
          
          if id is not None:
              for (k,v) in PREFIX_NORMALIZATION_MAP.items():
                  s = k+':'
                  if id.startswith(s):
                      return id.replace(s,v+':')
          return id
docs: E.g. MGI:MGI:nnnn --> MGI:nnnn