* Fix check for RIGHT_ATTRs in dep matcher
If a non-anchor node does not have RIGHT_ATTRS, the dep matcher throws
an E100, which says that non-anchor nodes must have LEFT_ID, REL_OP, and
RIGHT_ID. It specifically does not say RIGHT_ATTRS is required.
A blank RIGHT_ATTRS is also valid, and patterns with one will be
excepted. While not normal, sometimes a REL_OP is enough to specify a
non-anchor node - maybe you just want the head of another node
unconditionally, for example.
This change just sets RIGHT_ATTRS to {} if not present. Alternatively
changing E100 to state RIGHT_ATTRS is required could also be reasonable.
* Fix test
This test was written on the assumption that if `RIGHT_ATTRS` isn't
present an error will be raised. Since the proposed changes make it so
an error won't be raised this is no longer necessary.
* Revert test, update error message
Error message now lists missing keys, and RIGHT_ATTRS is required.
* Use list of required keys in error message
Also removes unused key param arg.
77d698dcae