[Rivet] UnstableFinalState::particlesByPt() not working?

[Kiran Joshi]

Hello,

When I do something like:
const ParticleVector& unstableFS = applyProjection<UnstableFinalState>(event, "UNSTABLE_FS").particlesByPt();
I find that the ParticleVector is empty.

However, when I instead do:
const ParticleVector& unstableFS = applyProjection<UnstableFinalState>(event, "UNSTABLE_FS").particles();
I can see the (several hundred) unstable final state particles that I expect to find.

I have been defining my UnstableFinalState as follows:
UnstableFinalState unstable_fs(-4.5, 4.5, 0.0*GeV);
addProjection(unstable_fs, "UNSTABLE_FS");

Is this a bug, or is particlesByPt() not supposed to be used with the UnstableFinalState?
(Or am I just implementing it incorrectly?)

Thanks,
Kiran