a problem about calculating relic density

hello ,i have a problem after i import my model and define darkmatter, i got a bug after i type generate relic density as followed:
Multiparticle labels:
all = g a ve vm vt ve~ vm~ vt~ u c t d s b u~ c~ t~ d~ s~ b~ z w+ zp h1 dsr ~dsi h2 fsdm ~vdm fvdm w- e- mu- ta- ~fdm e+ mu+ ta+
l- = e- mu-
dm_particle_0 = ~dsi
bsm = zp h1 dsr ~dsi h2
dm_particles = ~dsi dsr
j = g u c d s u~ c~ d~ s~
vl = ve vm vt
l+ = e+ mu+
p = g u c d s u~ c~ d~ s~
dm_particle_1 = dsr
vl~ = ve~ vm~ vt~
Command "generate relic density" interrupted with error:
AttributeError : 'NoneType' object has no attribute 'get'
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