Null fix

[texodus]

Fixed 'null' updates and initial loads.

[deepankarsharma]

See change to gnode_state.cpp lines 298-304 above: being able to express that is what the rest of the delta is about.

Thanks for the clarification, it was very helpful.

[texodus]

Thanks @sc1f and @neilslinger for the commits, as well as @deepankarsharma and @sl236 for reviewing!

I suspect there are more issues lurking with null support, but this is a substantial improvement already.