title: django admin saving inline with blank value
body: <p>I have two models as </p>
  
  <pre><code>class Employer(models.Model):
  ..
  ..
  
  
  class JobTitle(models.Model):
      type = models.IntegerField(null=False, choices=JobTitles.CHOICES,blank=True,default=0)
      employer = models.OneToOneField(Employer,unique=True,null=False)  
  </code></pre>
  
  <p>I have defined admin for <code>Employer</code> and defined <code>JobTitle</code> as inline class. </p>
  
  <p>However, when I saved an <code>Employer</code> object without selecting <code>JobTitle</code>, it raises the error <code>invalid literal for int() with base 10: ''</code> due to the <code>type</code> field of <code>JobTitle</code>.</p>
  
  <p>I would like to set <code>type</code> to 0, as I defined default=0, if I don't select any jobtitle when employer is saved.</p>
  
  <p>How can I achieve this ?</p>