itvideo It's due to the Gallery tab, the gallery is required field while you don't add images there so it noticed that error.
If you don't want this field is mandatory, you can edit file:
ROOT/templates/gk_royal/contenttype/types/gallery.xml
Look for this line of code:
<item name="src" type="media" preview="true" preview_width="100" preview_height="100" default="" label="PLG_JACONTENT_TYPE_IMAGE_LABEL" description="PLG_JACONTENT_TYPE_SELECT_AN_IMAGE_DESC" required="1" />
and change the attribute: required ="1" to required ="0"
