TDEM, Magnetic Permeability, muiMap

Why does TDEM (SimPEG.electromagnetics.time_domain.simulation.BaseTDEMSimulation) have no parameter “muiMap” (Mapping of Inverse Magnetic Permeability (m/H) to the inversion model., a SimPEG Map).
How to set Magnetic Permeability in TDEM.

http://docs.simpeg.xyz/content/em/api_FDEM.html#api

http://docs.simpeg.xyz/content/em/api_TDEM.html#module-SimPEG.electromagnetics.time_domain.simulation