def get_label(self, context):
        """Return this action's label.

        The label will change depending on whether or not the corresponding
        review request already has a diff.

        Args:
            context (django.template.Context):
                The collection of key-value pairs from the template.

        Returns:
            unicode: The label that displays this action to the user.
        """
        review_request = context['review_request']
        draft = review_request.get_draft(context['request'].user)

        if (draft and draft.diffset) or review_request.get_diffsets():
            return _('Update Diff')

        return _('Upload Diff')