browser.commands: Empty browser action reference causes conflicts

To provide users the ability for a keyboard shortcut to open extensions, you can define this in manifest:

"commands": {
    "_execute_browser_action": {
      "description": "Open extension popup"
    }
  },

This doesn't set a keyboard shortcut yet allows the user to assign one.

However, in iOS safari, when two extensions offer this functionality, the browser warns about it. See screenshot: