If the field is empty (has no value), the renderer outputs this, which is unsightly:
<a href="http://">http://</a> </div>
I believe this is because
template_preprocess_video_embed_field_embed_code() in video_embed_field.module doesn't check whether
$variables['url'] is empty before using it to build
$variables['embed_code'] ends up as the content of the "class="player"" div, above.
Attached is a patch that should fix this.