title: Django InlineModelAdmin gives error 'MediaDefiningClass' object is not iterable
body: <p>From models.py</p>
  
  <pre><code>class Indicator(models.Model):
      name = models.CharField(max_length=50)
      youtube = models.CharField(max_length=LONG_BLOG_POST_CHAR_LEN)
      description = models.CharField(max_length=LONG_BLOG_POST_CHAR_LEN)    
      recommendation = models.CharField(max_length=LONG_BLOG_POST_CHAR_LEN)
      isPublic = models.BooleanField(default=False)
      methods_path = models.CharField(max_length=100,default=None)
      meta_description = models.CharField(max_length=150,default='')
      image_path = models.CharField(max_length=100,blank=True)
  
      def __str__(self):
          return self.name   
  
  class IndicatorParameterInt(models.Model):
      name = models.CharField(max_length=50)
      value = models.IntegerField(default=1)
      indicator_int_parameter = models.ForeignKey(Indicator, on_delete=models.CASCADE)
      hidden = models.BooleanField(default=False)
  
  class IndicatorParameterFloat(models.Model):
      name = models.CharField(max_length=50)
      setting = models.FloatField(default=1)
      indicator_float_parameter = models.ForeignKey(Indicator, on_delete=models.CASCADE)
      hidden = models.BooleanField(default=False)
  
  class Comparison(models.Model):
      name = models.CharField(max_length=100)
  </code></pre>
  
  <p>From admin.py</p>
  
  <pre><code>from django.contrib import admin
  from .models import *
  
  # Register your models here.
  admin.site.register( MarketData )
  admin.site.register( Indicator )
  admin.site.register( UserProfile )
  
  
  
  class IndicatorParameterIntInline(admin.TabularInline):
      model = IndicatorParameterInt
      fk_name = "indicator_int_parameter"
  
  class IndicatorParameterFloatInline(admin.TabularInline):
      model = IndicatorParameterFloat
      fk_name = "indicator_float_parameter"   
  
  class ComparisonInline(admin.TabularInline):
      model = Comparison
      fk_name = "Comparison"  
  
  class IndicatorInline(admin.ModelAdmin):
      inlines = [ 
                  IndicatorParameterIntInline,
                  IndicatorParameterFloatInline,
                  ComparisonInline, 
                ]
  
  admin.site.unregister( Indicator )
  admin.site.register( IndicatorInline )
  </code></pre>
  
  <p>The error <strong>TypeError: 'MediaDefiningClass' object is not iterable</strong> comes up on the final line of admin: admin.site.register( IndicatorInline ). It doesn't matter if I try to register IndicatorInline first or any of the foreign key classes.</p>
  
  <p>I referenced <a href="https://stackoverflow.com/questions/7598524/django-admin-inline-model-for-user">this post</a>, which encouraged using the fk_name attribute. The error occurs regardless of whether or not I use fk_name.</p>