[Vue warn]: Error in render: "TypeError: Cannot read property 'map' of null"

[Decipher]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://gitpod.io/#github.com/Decipher/quickstart-druxt-site/tree/issue/menu_map_bug
2. Wait
3. See error

Expected behavior
Don't error.

Media

Your Environment (please complete the following information):
N/A

Additional context

druxt.js/packages/menu/src/components/DruxtMenu.vue

Lines 326 to 334 in 2847f69

	default: (attrs) => this.items.map((item) => h('DruxtMenuItem', {
	attrs,
	key: item.entity.id,
	props: {
	item,
	},
	})),
	}
	},