`one'(x)` errors, although `gradient(one, 0.0) === nothing` does not

[cossio]

using Zygote
julia> one'(0.0)
ERROR: MethodError: no method matching getindex(::Nothing, ::Int64)
Stacktrace:
 [1] (::Zygote.var"#59#60"{typeof(one)})(x::Float64)
   @ Zygote ~/.julia/packages/Zygote/FPUm3/src/compiler/interface.jl:83
 [2] top-level scope
   @ REPL[5]:1

[mcabbott]

This is only about the weird adjoint overload, gradient is fine:

julia> gradient(one, 0.0)

julia> one'(0.0)
ERROR: MethodError: no method matching getindex(::Nothing, ::Int64)