Django trans tag within a default filter

Does anyone know how this could properly be written in Django?

{{ m开发者_如何学Pythonu.expiry_date|default:"{% trans 'Free User' %}"}}

Obviously, the above does not work since it contains a tag within a tag's filter.

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Templates have an underscore syntax for translation also:

{{ mu.expiry_date|default:_("Free User")}}