NoReverseMatch while rendering

I got the following TemplateSyntaxError:

Caught NoReverseMatch while rendering: Reverse for 'profile_detail'
with arguments '('',)' and keyword arguments '{}' not found.

The exact line causing the issue is the following in my
view_phone.html template file:

<div class="details">{% blocktrans %}added by{% endblocktrans %} <a
href="{% url profile_detail phone.adder.username %}">{{ phone.adder }}
</a></div>{% blocktrans %}on{% endblocktrans %} {{ phone.added|date }}

Has anyone seen this before? My urls.py seem to be configured properly
etc. Can't seem to figure this one out.

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