See https://github.com/dwavesystems/dwave-optimization/blob/1ea1a05c1d10f0698abb6398f4fa0d05a37e4d7a/dwave/optimization/_model.pyx#L1580-L1581 Should have been part of https://github.com/dwavesystems/dwave-optimization/pull/468, or at least should have a meaningful error message.
See
dwave-optimization/dwave/optimization/_model.pyx
Lines 1580 to 1581 in 1ea1a05
Should have been part of #468, or at least should have a meaningful error message.