first failed test

### Also not a PR

This 'failed test' comes complete with the logfile of the broker, and a description of the test (see the file SUBS_PATH), including contents in mongo after the test.

## Will NOT be merged, but discarded after discussion


I think here is the problem. Try using

```
entities.type: ""
```

Note that is is not the same an entity having type "" that not having type (i.e. no subfield `type` in the `_id` field in DB).