code: def is_unit_exist(unit_id):
      
      attribute = 'objectClass'
      response = LDAP_search(
          pattern_search="(uniqueidentifier={})".format(unit_id),
          attribute=attribute
      )
      try:
          unit_exist = 'EPFLorganizationalUnit' in response[0]['attributes'][attribute]
      except Exception:
          return False
  
      return unit_exist
docs: Return True if the unit 'unid_id' exists.
      Otherwise return False