Resolve #3379091 "Nodetype post required values"

Closes #3379091

core/modules/book/config/optional/node.type.book.yml

@@ -7,7 +7,7 @@ dependencies:
 name: 'Book page'
 type: book
 description: '<em>Books</em> have a built-in hierarchical navigation. Use for handbooks or tutorials.'
-help: ''
+help: null
 new_revision: true
 preview_mode: 1
 display_submitted: true