Cannot delete undefined subscriptions

When I create a subscription and than press the trashcan icon, nothing happens.

Steps to repeat:

1. Start reactotron
2. Reload app
3. Click on the "State" button on the sidebar.
4. Create a subscription called "foo" (that no corresponding mobx-state-tree foo store), which will created a list entry in state section that is marked as "undefined".
5. Hit click the trashcan button on the list. Observe that nothing happens.

Expected behavior:

An undefined subscription should deletable when the trash button is clicked.

Start in the Reactotron State sidebar entry point and reproduce the issue by creating an undefined "foo" subscription, then clicking its trashcan. Trace the deletion behavior for that list entry and verify that the undefined subscription is removed when the trash button is clicked; add or run the relevant UI test if one is found.

Written by the indexing model from the issue text.