title: Symfony2 ContextErrorException
body: <p>I have in my entity a method:</p>
  
  <pre><code>public function getProviderAvailabilities($providerKey)
  </code></pre>
  
  <p>When i try add a form field by <code>$builder-&gt;add('ProviderAvailabilities')</code> I get the following error </p>
  
  <blockquote>
    <p>ContextErrorException: Warning: Missing argument 1 for
    getProviderAvailabilities() called in
    Symfony/Component/PropertyAccess/PropertyAccessor.php on line 211 and
    defined in </p>
  </blockquote>
  
  <p>How can I fix it? PS. Sorry for my English.</p>