code: def get_mnemonic(self, mnemonic, alias=None):
          
          alias = alias or {}
          aliases = alias.get(mnemonic, [mnemonic])
          for a in aliases:
              if a in self.data:
                  return a
          return None
docs: Instead of picking curves by name directly from the data dict, you
          can pick them up with this method, which takes account of the alias
          dict you pass it. If you do not pass an alias dict, then you get the
          curve you asked for, if it exists, or None. NB Wells do not have alias
          dicts, but Projects do.
  
          Args:
              mnemonic (str): the name of the curve you want.
              alias (dict): an alias dictionary, mapping mnemonics to lists of
                  mnemonics.
  
          Returns:
              Curve.