The following code

```
using Zygote
gradient(x -> sum(map(sum, eachcol(x))), rand(3, 4))
```

gives the error message

ERROR: Need an adjoint for constructor Base.Generator{Base.OneTo{Int64}, Base.var"#193#194"{Matrix{Float64}}}. Gradient is of type Vector{FillArrays.Fill{Float64, 1, Tuple{Base.OneTo{Int64}}}}

However if I add a `collect`

function to the results of `eachcol`

, I can get the correct gradient.

```
gradient(x -> sum(map(sum, collect(eachcol(x)))), rand(3, 4))
```

Is this a limitation of Zygote, or did I use it wrong? Thanks!