Fiber!(SparseList(Element(missing)), Union{Missing, Float64}[2.0, missing, missing, 1.0, 3.0, missing]):
Fiber(SparseList{Int32}(Element{missing, Union{Missing, Float64}, Int32}(Union{Missing, Float64}[2.0, 1.0, 3.0]), 6, [1, 4], [1, 4, 5]))

