title: Django admin: 'bool' object has no attribute 'startswith'
body: <p>I am using django_smart_select package. I am getting the following error for the model in which I am trying to use the chained select option.   </p>
  
  <pre><code>AttributeError at /admin/tags/tag/add/
  'bool' object has no attribute 'startswith'
  Request Method: GET
  Request URL:    http://127.0.0.1:8000/admin/tags/tag/add/
  Django Version: 1.11.4
  Exception Type: AttributeError
  Exception Value:    
  'bool' object has no attribute 'startswith'
  
  Error during template rendering
  
  In template C:\Users\gautammandewalker\Envs\django01\lib\site-
  packages\django\contrib\admin\templates\admin\base.html, error at line 3
  'bool' object has no attribute 'startswith'
  1   {% load i18n static %}&lt;!DOCTYPE html&gt;
  2   {% get_current_language as LANGUAGE_CODE %}{% get_current_language_bidi 
  as LANGUAGE_BIDI %}
  3   &lt;html lang="{{ LANGUAGE_CODE|default:"en-us" }}" {% if LANGUAGE_BIDI 
  %}dir="rtl"{% endif %}&gt;
  4   &lt;head&gt;
  5   &lt;title&gt;{% block title %}{% endblock %}&lt;/title&gt;
  6   &lt;link rel="stylesheet" type="text/css" href="{% block stylesheet %}{% 
  static "admin/css/base.css" %}{% endblock %}" /&gt;
  7   {% block extrastyle %}{% endblock %}
  8   {% if LANGUAGE_BIDI %}&lt;link rel="stylesheet" type="text/css" href="{% 
  block stylesheet_rtl %}{% static "admin/css/rtl.css" %}{% endblock %}" /&gt;{% 
  endif %}
  9   {% block extrahead %}{% endblock %}
  10  {% block blockbots %}&lt;meta name="robots" content="NONE,NOARCHIVE" /&gt;{% 
   endblock %}
  11  &lt;/head&gt;
  12  {% load i18n %}
  </code></pre>