title: How to save a field added in the clean() method?
body: <p>My form has <code>first_name</code> and <code>last_name</code> fields, but my model has just a <code>name</code> field. In the <code>clean()</code> method of the form I set <code>self.cleaned_data['name']</code>, but when I try to save it I get this error:</p>
  
  <pre><code>&lt;ul class="errorlist"&gt;&lt;li&gt;name&lt;ul class="errorlist"&gt;&lt;li&gt;This field is required.&lt;/li&gt;&lt;/ul&gt;&lt;/li&gt;&lt;/ul&gt;
  </code></pre>
  
  <p>If I exclude it,</p>
  
  <pre><code>class Meta:
      model = UserProfile
      exclude = ('name',)
  </code></pre>
  
  <p>however, then it doesn't get saved.</p>
  
  <p>So how do I get it to both save, and not throw an error?</p>