After creating a navigation block and adding a few items, it doesn't seem possible to un-link them.

Gutenberg version tested: 7.0.0

To reproduce
Steps to reproduce the behavior:

1. Add a new page, and add a navigation block
2. Add a few items to the block, making sure they're linked pages
3. Save/publish the page
4. Attempt to unlink an item by modifying it and deleting the listed page
5. Notice appears to fill in the field. Clicking away from the field closes it and loses the modification (removal)

Expected behavior
I would have expected to be able to modify the link, to prevent the link from being active!

Screenshots

Chrome:

Firefox:

Desktop (please complete the following information):

• OS: macOS Mojave 10.14.6
• Browser: Chrome 78.0.3904.108, also tested on Firefox 70.0.1

I've not yet tested on a smartphone!