updating griewank

Author: arnavk23

src/ADNLPProblems/griewank.jl

@@ -1,12 +1,12 @@
 export griewank
 
-function griewank(; n::Int = default_nvar, type::Type{T} = Float64, x0::AbstractVector{T} = T[], kwargs...) where {T}
+function griewank(; n::Int = default_nvar, type::Type{T} = Float64, x0::Union{Nothing, AbstractVector{T}} = nothing, kwargs...) where {T}
   function f(x)
     n = length(x)
     sum_term = sum(x[i]^2 for i = 1:n) / 4000
     prod_term = prod(cos(x[i] / sqrt(T(i))) for i = 1:n)
     return sum_term - prod_term + 1
   end
-  x0_local = isempty(x0) ? zeros(T, n) : x0
+  x0_local = isnothing(x0) ? zeros(T, n) : x0
   return ADNLPModels.ADNLPModel(f, x0_local, name = "griewank"; kwargs...)
 end