Fiber!(SparseList(Element(NaN)), [2.0, NaN, NaN, 1.0, 3.0, NaN]):
Fiber(SparseList{Int64, Int64}(Element{NaN, Float64, Int64, Vector{Float64}}([2.0, 1.0, 3.0]), 6, [1, 4], [1, 4, 5]))

