UNet inchannels != 3 not working

[nickkeepfer]

It seems the UNet implementation only works with inputs with channel-size 3

Status `/private/var/folders/98/8xz00xq10hq7kdrdvdjd1jy00000gn/T/jl_EZ324U/Project.toml`
  [dbeba491] Metalhead v0.8.0
  [44cfe95a] Pkg v1.8.0

using Metalhead
UNet((128,128),1,3,Metalhead.backbone(DenseNet(121)))

ERROR: DimensionMismatch: layer Conv((7, 7), 3 => 64, pad=3, stride=2, bias=false) expects size(input, 3) == 3, but got 128×128×1×1 Array{Flux.NilNumber.Nil, 4}