type of `db.reg.root_map` changed

[tacaswell]

Expected Behavior

type(db.reg.root_map)

should be dict to be compatible with the previous behavior.

Current Behavior

In now in None

Possible Solution

The property that warns should return an empty dict not None

Steps to Reproduce (for bugs)

1. see above

Context

Your Environment

databroker: '2.0.0b10' in the "scientific python" image on NSLS-II jupyterhub