ConvTranspose gradient error: no method matching iterate(::Nothing)

[jumerckx]

This code fails with ERROR: MethodError: no method matching iterate(::Nothing)

using Flux

m = ConvTranspose((3,3), 2=>1)
x = rand(10,10,2,1)

gradient(()->sum(m(x)), params(m))

Here's the full stacktrace:

julia> gradient(()->sum(m(x)), params(m))
ERROR: MethodError: no method matching iterate(::Nothing)
Closest candidates are:
  iterate(::Core.SimpleVector) at essentials.jl:568
  iterate(::Core.SimpleVector, ::Any) at essentials.jl:568
  iterate(::ExponentialBackOff) at error.jl:199
  ...
Stacktrace:
 [1] _zip_iterate_some at .\iterators.jl:350 [inlined]
 [2] _zip_iterate_all at .\iterators.jl:342 [inlined]
 [3] iterate at .\iterators.jl:332 [inlined]
 [4] iterate at .\generator.jl:44 [inlined]
 [5] collect(::Base.Generator{Base.Iterators.Zip{Tuple{Array{typeof(∂(λ)),1},Nothing}},getfield(Base, Symbol("##3#4")){getfield(Zygote, Symbol("##945#949"))}}) at .\array.jl:606
 [6] map(::Function, ::Array{typeof(∂(λ)),1}, ::Nothing) at .\abstractarray.jl:2091
 [7] (::getfield(Zygote, Symbol("##944#948")){Array{typeof(∂(λ)),1}})(::Nothing) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\lib\array.jl:121
 [8] (::getfield(Zygote, Symbol("##952#953")){getfield(Zygote, Symbol("##944#948")){Array{typeof(∂(λ)),1}}})(::Nothing) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\lib\array.jl:136
 [9] getindex at .\tuple.jl:26 [inlined]
 [10] (::typeof(∂(getindex)))(::Nothing) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\compiler\interface2.jl:0
 [11] (::typeof(∂(Flux.conv_transpose_dims)))(::Nothing) at C:\Users\jules\.julia\packages\Flux\WxpHb\src\layers\conv.jl:109
 [12] (::typeof(∂(λ)))(::FillArrays.Fill{Float64,4,NTuple{4,Base.OneTo{Int64}}}) at C:\Users\jules\.julia\packages\Flux\WxpHb\src\layers\conv.jl:124
 [13] #27 at .\none:1 [inlined]
 [14] (::typeof(∂(getfield(Main, Symbol("##27#28"))())))(::Float64) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\compiler\interface2.jl:0
 [15] (::getfield(Zygote, Symbol("##38#39")){Zygote.Params,Zygote.Context,typeof(∂(getfield(Main, Symbol("##27#28"))()))})(::Float64) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\compiler\interface.jl:101
 [16] gradient(::Function, ::Zygote.Params) at C:\Users\jules\.julia\packages\Zygote\lRotY\src\compiler\interface.jl:47
 [17] top-level scope at none:0

[MikeInnes]

Due to an issue in this function. We could just @nograd, but it'd be good to figure out why Zygote is failing here.

[xukai92]

Yes for now I just do Flux.Zygote.@nograd Flux.conv_transpose_dims to fix this.

[kczimm]

My problem led me to this issue which results in the same error. If it's not a bug but me, perhaps it should stay here or otherwise go in a different issue? I'm not sure.

using Flux

m = Dense(2, 2, x->log.(max.(eps.(x), x)))
x = rand(2)

gradient(()->sum(m(x)), params(m))

ERROR: LoadError: MethodError: no method matching iterate(::Nothing)
Closest candidates are:
  iterate(!Matched::Core.SimpleVector) at essentials.jl:600
  iterate(!Matched::Core.SimpleVector, !Matched::Any) at essentials.jl:600
  iterate(!Matched::ExponentialBackOff) at error.jl:218
  ...
Stacktrace:
 [1] (::Zygote.var"#1589#1591"{Zygote.var"#59#78"})(::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/lib/broadcast.jl:140
 [2] (::Zygote.var"#3946#back#1592"{Zygote.var"#1589#1591"{Zygote.var"#59#78"}})(::Float32) at /home/kevin/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
 [3] (::Zygote.var"#157#158"{Zygote.var"#3946#back#1592"{Zygote.var"#1589#1591"{Zygote.var"#59#78"}},Tuple{Tuple{Nothing,Nothing,Nothing},Tuple{}}})(::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/lib/lib.jl:156
 [4] (::Zygote.var"#297#back#159"{Zygote.var"#157#158"{Zygote.var"#3946#back#1592"{Zygote.var"#1589#1591"{Zygote.var"#59#78"}},Tuple{Tuple{Nothing,Nothing,Nothing},Tuple{}}}})(::Float32) at /home/kevin/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
 [5] broadcasted at ./broadcast.jl:1231 [inlined]
 [6] #7 at /tmp/mwe.jl:3 [inlined]
 [7] (::typeof(∂(#7)))(::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface2.jl:0
 [8] (::Zygote.var"#1576#1583")(::typeof(∂(#7)), ::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/lib/broadcast.jl:129
 [9] (::Base.var"#3#4"{Zygote.var"#1576#1583"})(::Tuple{typeof(∂(#7)),Float32}) at ./generator.jl:36
 [10] iterate at ./generator.jl:47 [inlined]
 [11] collect at ./array.jl:622 [inlined]
 [12] map at ./abstractarray.jl:2155 [inlined]
 [13] (::Zygote.var"#1575#1582"{Tuple{Array{Float32,1}},Val{2},Array{typeof(∂(#7)),1}})(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/Zygote/oMScO/src/lib/broadcast.jl:129
 [14] (::Zygote.var"#3934#back#1586"{Zygote.var"#1575#1582"{Tuple{Array{Float32,1}},Val{2},Array{typeof(∂(#7)),1}}})(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
 [15] (::Zygote.var"#157#158"{Zygote.var"#3934#back#1586"{Zygote.var"#1575#1582"{Tuple{Array{Float32,1}},Val{2},Array{typeof(∂(#7)),1}}},Tuple{Tuple{Nothing,Nothing,Nothing},Tuple{}}})(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/Zygote/oMScO/src/lib/lib.jl:156
 [16] (::Zygote.var"#297#back#159"{Zygote.var"#157#158"{Zygote.var"#3934#back#1586"{Zygote.var"#1575#1582"{Tuple{Array{Float32,1}},Val{2},Array{typeof(∂(#7)),1}}},Tuple{Tuple{Nothing,Nothing,Nothing},Tuple{}}}})(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/ZygoteRules/6nssF/src/adjoint.jl:49
 [17] broadcasted at ./broadcast.jl:1231 [inlined]
 [18] Dense at /home/kevin/.julia/packages/Flux/2i5P1/src/layers/basic.jl:102 [inlined]
 [19] (::typeof(∂(invoke)))(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface2.jl:0
 [20] Dense at /home/kevin/.julia/packages/Flux/2i5P1/src/layers/basic.jl:113 [inlined]
 [21] (::typeof(∂(λ)))(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface2.jl:0
 [22] Dense at /home/kevin/.julia/packages/Flux/2i5P1/src/layers/basic.jl:116 [inlined]
 [23] (::typeof(∂(λ)))(::FillArrays.Fill{Float32,1,Tuple{Base.OneTo{Int64}}}) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface2.jl:0
 [24] #9 at /tmp/mwe.jl:6 [inlined]
 [25] (::typeof(∂(#9)))(::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface2.jl:0
 [26] (::Zygote.var"#38#39"{Zygote.Params,Zygote.Context,typeof(∂(#9))})(::Float32) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface.jl:101
 [27] gradient(::Function, ::Zygote.Params) at /home/kevin/.julia/packages/Zygote/oMScO/src/compiler/interface.jl:47
 [28] top-level scope at /tmp/mwe.jl:6
 [29] include at ./boot.jl:328 [inlined]
 [30] include_relative(::Module, ::String) at ./loading.jl:1105
 [31] include(::Module, ::String) at ./Base.jl:31
 [32] exec_options(::Base.JLOptions) at ./client.jl:287
 [33] _start() at ./client.jl:460

I'm running Ubuntu with Julia v1.3.0 and Flux v0.10.1.