Before return false, I would include a LM_E trace, as in other cases, e.g.:

```
*err = "Generic Exception from mongo";
LM_RE(false, ("Database error: '%s'", err->c_str()));
```
(See also https://github.com/telefonicaid/fiware-orion/pull/246/files#r10160789 about including the message from the exception, if possible).