Some curve objects don't have an evaluated mesh at all, but line art currently assumes that all curve objects have one before converting it to a mesh internally. Fix this by checking if the curve object has an evaluated mesh before skipping it. The remaining problem is that evalauted from non-mesh objects or evaluated curves from non-curve objects, etc. will be ignored if "Allow Duplicates" is off. That's a different problem though. Differential Revision: https://developer.blender.org/D14036