use zero_tangent for _instantiate_zeros

Author: oxinabox

src/rulesets/Base/array.jl

@@ -71,9 +71,7 @@ materialises each zero `ẋ` to be `zero(x)`.
 """
 _instantiate_zeros(ẋs, xs) = map(_i_zero, ẋs, xs)
 _i_zero(ẋ, x) = ẋ
-_i_zero(ẋ::AbstractZero, x) = zero(x)
-# Possibly this won't work for partly non-diff arrays, something like `gradient(x -> ["abc", x][end], 1)`
-# may give a MethodError for `zero` but won't be wrong.
+_i_zero(ẋ::AbstractZero, x) = zero_tangent(x)
 
 # Fast paths. Should it also collapse all-Zero cases?
 _instantiate_zeros(ẋs::Tuple{Vararg{Number}}, xs) = ẋs