Freeform - make file_upload field required

Question

I'm trying to create a form with Freeform Pro containing a File Upload field that is required. So the form should only submit when the user actually uploads a file.

Setting the field to required in template parameter seems to have no effect.

Bug or missing feature? Any workarounds?

{exp:freeform:form form_name="feedback" secure_action="yes" secure_return="yes" required="some_picture|email" form:id="some_form" admin_notification_template="feedback_notify" admin_notify="foobar@example.com" prevent_duplicate_on="email" inline_error_return="group/template" inline_errors="yes" return="group/feedback_thanx"}

<label for="fmail">
<span class="frage"{if freeform:error:email} style="color:red;"{/if}> E-MAIL </span>
{freeform:field:email id="fmail"}
</label>

<label for="some_picture">
<span class="frage" {if freeform:error:some_picture}style="color:red;"{/if}>Please upload! </span><br><br>
{freeform:field:some_picture id="some_picture"}
</label>

<input type="submit" name="submit" value="Absenden" />
{/exp:freeform:form} 

Answer 1

You can make it required by adding an hidden input with the same name as your file input:

{exp:freeform:form required="file_upload"}

  {freeform:field:file_upload show="1"}
  <input type="hidden" name="file_upload">

  <button type="submit">Send</button>

{/exp:freeform:form}