def exists_evaluator(self, index):
    """ Evaluate the given exists match condition for the user attributes.

      Args:
        index: Index of the condition to be evaluated.

      Returns:
        Boolean: True if the user attributes have a non-null value for the given condition,
                 otherwise False.
    """
    attr_name = self.condition_data[index][0]
    return self.attributes.get(attr_name) is not None