from-to for roots

[fcbond]

Currently roots end up with kara and made values of None, should be sentence start and sentence end.

Not sure if this should be considered a PyDelphin issue as well: @goodmami
We get the values from node.start and node.end. Probably not :-)

[goodmami]

If it's a PyDelphin issue, I'll need more info, as None is a valid value of node.start and node.end when the position information is not provided in the derivation string. E.g., show me an example derivation causing the issue and minimal code to reproduce the problem.