NaN in gradient of abs() on complex 0

[koenvos]

using Zygote
x = [0f0 + 1im * 0f0]
f(x) = sum(abs.(x))
f'(x)

result:
1-element Vector{ComplexF32}:
NaN32 + NaN32*im

[koenvos]

Seems like it's caused by the sqrt() (on the sum of squared real and imaginary parts).
Fixed by adding a small offset:
abs_(x::Complex) = sqrt(real(x) ^ 2 + imag(x) ^ 2 + 1f-12)