as reported by dadoirie in https://github.com/FirEmerald/AdditionalPlacements/issues/34
this is caused by the "additional placement" blocks having the same item as the original blocks they came from. Despite occupying distinctly unique pairings inside the original mappings, when converted to item-to-item mappings, they resolve to the same pairing, which causes the google collections library to throw an exception.
Relevant version information can be found in the original issue, though I would assume it can be reproduced on earlier versions.
as reported by dadoirie in https://github.com/FirEmerald/AdditionalPlacements/issues/34 this is caused by the "additional placement" blocks having the same item as the original blocks they came from. Despite occupying distinctly unique pairings inside the original mappings, when converted to item-to-item mappings, they resolve to the same pairing, which causes the google collections library to throw an exception. Relevant version information can be found in the original issue, though I would assume it can be reproduced on earlier versions.