Monty.Frameworks.Environments.PositioningProcedures.ObjectNotVisibleError exception (ExTbpMonty.Core v0.1.0)

Raised when a single-object scene shows no object to position against.

Mirrors tbp/monty/frameworks/environments/positioning_procedures.py::ObjectNotVisibleError. A multi-object scene treats "the target is not in view" as an answer — the procedure declines to move and the episode starts from where it is — but a single-object scene has nothing else to look at, so it is a fault in how the episode was set up.