a problem about DonCare

[pxs7]

I have new a module as follow，
val mod = Module(fuGen(null, 0)) mod.io <> DontCare mod io was set dontcare and output is not needed， in theory， mod should be removed in transalated verilog. but it appears in verilog. How can i remove in finnal rtl, (my purpose is to use some function in mod)