code: def remove(self, tag, nth=1):
          
  
          tag = fix_tag(tag)
          nth = int(nth)
  
          for i in range(len(self.pairs)):
              t, v = self.pairs[i]
              if t == tag:
                  nth -= 1
                  if nth == 0:
                      self.pairs.pop(i)
                      return v
  
          return None
docs: Remove the n-th occurrence of tag in this message.
  
          :param tag: FIX field tag number to be removed.
          :param nth: Index of tag if repeating, first is 1.
          :returns: Value of the field if removed, None otherwise.