In src/PooledArrays.jl at lines 202-203, we find the following code

@inline PooledArray(t::Type) = PooledArray(Array(t,0))
@inline PooledArray(t::Type, r::Type) = PooledArray(Array(t,0), r)

which does not work as there is no method Array(::Type,::Int).

I guess the intent was more like Array{t}(undef,0) (or just t[]) instead of Array(t,0).