salt: Exception when using Salt mine from pillar

$ salt 'apt-mirror' state.highstate
apt-mirror:
    Data failed to compile:
----------
    Pillar failed to render with the following messages:
----------
    Rendering SLS 'apt-repo.eu-west-1' failed, render error:
Jinja error: 'master_uri'
Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/salt/utils/templates.py", line 261, in render_jinja_tmpl
    output = jinja_env.from_string(tmplstr).render(**unicode_context)
  File "/usr/lib/python2.7/dist-packages/jinja2/environment.py", line 894, in render
    return self.environment.handle_exception(exc_info, True)
  File "<template>", line 1, in top-level template code
  File "/usr/lib/pymodules/python2.7/salt/modules/mine.py", line 182, in get
    auth = _auth()
  File "/usr/lib/pymodules/python2.7/salt/modules/mine.py", line 24, in _auth
    __context__['auth'] = salt.crypt.SAuth(__opts__)
  File "/usr/lib/pymodules/python2.7/salt/crypt.py", line 502, in __init__
    self.crypticle = self.__authenticate()
  File "/usr/lib/pymodules/python2.7/salt/crypt.py", line 514, in __authenticate
    self.opts.get('_safe_auth', True)
  File "/usr/lib/pymodules/python2.7/salt/crypt.py", line 345, in sign_in
    if self.opts['master_ip'] not in self.opts['master_uri']:
KeyError: 'master_uri'

; line 1

---
{% set ipaddrs = salt['mine.get']('apt-mirror', 'network.ipaddrs')[0] %}    <======================
{% if ipaddrs %}
apt-repo: http://{{ ipaddrs[0] }}
{% else %}
apt-repo: http://packages.somewhere.com
{% endif %}
[...]

---

This works:

$ salt 'apt-mirror' mine.get apt-mirror network.ipaddrs
apt-mirror:
    ----------

(no, I wasn’t expecting any data, nor an exception)