Possible vcat bug?

Asking before opening an issue, should I? MWE:

julia> VERSION
v"1.1.0-DEV.298"

julia> vcat(Nothing[], [missing], [1.0], [Int8(1)])
ERROR: MethodError: convert(::Type{Union{Missing, Nothing, Float64}}, ::Int8) is ambiguous. Candidates:
  convert(::Type{Union{Missing, T}}, x) where T in Base at missing.jl:43
  convert(::Type{Union{Nothing, T}}, x) where T in Base at some.jl:21
Possible fix, define
  convert(::Type{Union{Missing, Nothing}}, ::Any)