code: def handle_exists(self, spec, checkable):
          '''The implementation of this one is weird. By the time
          the {'$exists': True} spec gets to the dispatched
          handler, the key presumably exists.
  
          So we just parrot the assertion the spec makes. If it
          asserts the key exists, we return True. If it asserts
          the key doesn't exist, we return False, because that
          can't be true.
          '''
          if not isinstance(spec, bool):
              msg = 'The argument of an exists query must be of type bool.'
              raise InvalidQuery(msg)
          return spef handle_exists(self, spec, checkable):
          '''The implementation of this one is weird. By the time
          the {'$exists': True} spec gets to the dispatched
          handler, the key presumably exists.
  
          So we just parrot the assertion the spec makes. If it
          asserts the key exists, we return True. If it asserts
          the key doesn't exist, we return False, because that
          can't be true.
          '''
          if not isinstance(spec, bool):
              msg = 'The argument of an exists query must be of type bool.'
              raise InvalidQuery(msg)
          return spec
docs: The implementation of this one is weird. By the time
          the {'$exists': True} spec gets to the dispatched
          handler, the key presumably exists.
  
          So we just parrot the assertion the spec makes. If it
          asserts the key exists, we return True. If it asserts
          the key doesn't exist, we return False, because that
          can't be true.