make ∇eachslice accept AbstractZero (#639)

* make ∇eachslice accept Zero

* bump

Author: mcabbott

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.36.1"
+version = "1.36.2"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/rulesets/Base/indexing.jl

@@ -93,6 +93,7 @@ function ∇eachslice(dys_raw, x::AbstractArray, vd::Val{dim}) where {dim}
     end
     return ProjectTo(x)(dx)
 end
+∇eachslice(dys::AbstractZero, x::AbstractArray, vd::Val{dim}) where {dim} = dys
 
 _zero_fill!(dx::AbstractArray{<:Number}) = fill!(dx, zero(eltype(dx)))
 _zero_fill!(dx::AbstractArray) = map!(zero, dx, dx)