code: def make_indicator_node(operator, nid=None):
      
      if operator.upper() not in VALID_INDICATOR_OPERATORS:
          raise ValueError('Indicator operator must be in [{}].'.format(VALID_INDICATOR_OPERATORS))
      i_node = et.Element('Indicator')
      if nid:
          i_node.attrib['id'] = nid
      else:
          i_node.attrib['id'] = ioc_et.get_guid()
      i_node.attrib['operator'] = operator.upper()
      return i_node
docs: This makes a Indicator node element.  These allow the construction of a logic tree within the IOC.
  
      :param operator: String 'AND' or 'OR'.  The constants ioc_api.OR and ioc_api.AND may be used as well.
      :param nid: This is used to provide a GUID for the Indicator. The ID should NOT be specified under normal circumstances.
      :return: elementTree element