Incorrect nothing gradient

[juliohm]

MWE:

julia> using Zygote

julia> f(x, y) = y
f (generic function with 1 method)

julia> gradient(f, 0, 0)
(nothing, 1.0)

On a fresh environment with the latest stable release of Zygote.jl

[CarloLucibello]

Zygote can return nothing in place of zero, this is expected

[juliohm]

Thank you @CarloLucibello for clarifying this. Shouldn't this nothing value be handled for end-users though with multiple dispatch? It becomes difficult to write generic math when nothing is returned sometimes.

As people suggested on Zulip, one could define:

denothing(x) = x
denothing(::Nothing) = 0.0

to automatically return 0.0 in all cases?

[CarloLucibello]

Nothing can be returned in correspondence of variables of any type (numbers, arrays, custom types) so take that into account.

[juliohm]

Should there be a special Zero singleton type that behaves like zero every time? Why can't we rely on zero(T) for example?