Test changes from FluxML/ZygoteRules.jl#26

Author: ToucheSir

src/Zygote.jl

@@ -6,6 +6,11 @@ using LinearAlgebra: copytri!, AbstractTriangular
 import ZygoteRules: @adjoint, @adjoint!, AContext, adjoint, _pullback, pullback,
   literal_getproperty, literal_getfield, unthunk_tangent
 
+ZygoteRules.gradtuple0(::Tuple{Vararg{Nothing}}) = nothing
+ZygoteRules.gradtuple1(::Tuple{Vararg{Nothing}}) = nothing
+ZygoteRules.gradtuple2(::Tuple{Vararg{Nothing}}) = nothing
+ZygoteRules.gradtuple3(::Tuple{Vararg{Nothing}}) = nothing
+
 using ChainRulesCore
 using ChainRules: ChainRules, rrule, unthunk, canonicalize
 using IRTools