Attribute alt on image from menu-item

Hello,

I have a problem with the plugin, in the menu part, the images where are located there (thumbnails), are without attribute “alt”, at the wp-admin in Appareance > Menu on the “Posts” category there is a:
<div class=”img_content”>%post_featured_image_thumb</div>%post_title
where %post_featured_image_thumb bring the image tag thumbnail but not the attribute “alt”,

Someone knows what it can be?

Thank you!