" 'irls_threshold' must be a value in the range (0.0, inf]"

Dear all:
I am doing some inversion test using spontaneous_potential moudel within simpeg.
When I use the sparse regularization class to constrain the inversion result using an IRLS approach,
I got a mistake " ‘irls_threshold’ must be a value in the range (0.0, inf]"
and the closed file is the case I build, could you help me adress this issues?

thanks in advace.