Error with acyclic coloring

[amontoison]

We should add init=0 here before that we release a new version.
I got an error with ADNLPModels.jl:

Basic Hessian of residual derivative with backend=ADNLPModels.SparseReverseADHessian and T=Float64: Error During Test at /home/alexis/Bureau/git/ADNLPModels.jl/test/sparse_hessian_nls.jl:20
  Got exception outside of a @test
  MethodError: reducing over an empty collection is not allowed; consider supplying `init` to the reducer
  Stacktrace:
    [1] reduce_empty(op::Base.MappingRF{typeof(length), typeof(max)}, ::Type{Vector{Int64}})
      @ Base ./reduce.jl:361
    [2] reduce_empty_iter
      @ ./reduce.jl:384 [inlined]
    [3] mapreduce_empty_iter(f::Function, op::Function, itr::Vector{Vector{Int64}}, ItrEltype::Base.HasEltype)
      @ Base ./reduce.jl:380
    [4] _mapreduce(f::typeof(length), op::typeof(max), ::IndexLinear, A::Vector{Vector{Int64}})
      @ Base ./reduce.jl:432
    [5] _mapreduce_dim
      @ ./reducedim.jl:365 [inlined]
    [6] mapreduce
      @ ./reducedim.jl:357 [inlined]
    [7] SparseMatrixColorings.TreeSetColoringResult(S::SparseMatrixCSC{Bool, Int64}, color::Vector{Int64}, tree_set::SparseMatrixColorings.TreeSet, decompression_eltype::Type{Float64})
      @ SparseMatrixColorings ~/Bureau/git/SparseMatrixColorings.jl/src/result.jl:282
    [8] coloring(A::SparseMatrixCSC{Bool, Int64}, ::ColoringProblem{:symmetric, :column}, algo::GreedyColoringAlgorithm{:substitution, NaturalOrder}; decompression_eltype::Type)
      @ SparseMatrixColorings ~/Bureau/git/SparseMatrixColorings.jl/src/interface.jl:227
    [9] coloring
      @ ~/Bureau/git/SparseMatrixColorings.jl/src/interface.jl:218 [inlined]
   [10] ADNLPModels.SparseReverseADHessian(nvar::Int64, f::Function, ncon::Int64, c!::var"#F!#47", H::SparseMatrixCSC{Bool, Int64}; x0::Vector{Float64}, coloring_algorithm::GreedyColoringAlgorithm{:substitution, NaturalOrder}, kwargs::@Kwargs{})
      @ ADNLPModels ~/Bureau/git/ADNLPModels.jl/src/sparse_hessian.jl:153