handle empty accordions differently

There are many places in inventory where the contents of an accordion are conditional. The <Accordion> class defines children as a required property, however, so this generates a console warning when the conditional evaluates false. We have two options, maybe three:

1. hide the accordion when it's empty
2. show a "no content" message when no content is available
3. don't make Accordion.children a required property

Which is preferred?