construct empty vector with `StructVector{Foo1}()`

julia> struct Foo1
           x::Int
           y::Int
       end

julia> Vector{Foo1}()
Foo1[]

julia> StructVector{Foo1}()
ERROR: type NamedTuple has no field x
Stacktrace:
 [1] (::Base.var"#164#167"{(:x, :y), NamedTuple{(), Tuple{}}})(n::Int64)
   @ Base ./none:0
 [2] iterate
   @ ./generator.jl:47 [inlined]
 [3] (NamedTuple{(:x, :y), T} where T<:Tuple)(nt::NamedTuple{(), Tuple{}})
   @ Base ./namedtuple.jl:99
 [4] (StructArray{Foo1, N, C, I} where {N, C<:Union{Tuple, NamedTuple}, I})(c::NamedTuple{(), Tuple{}})
   @ StructArrays ~/repos/StructArrays.jl/src/structarray.jl:92
 [5] #_#5
   @ ~/repos/StructArrays.jl/src/structarray.jl:100 [inlined]
 [6] StructArray
   @ ~/repos/StructArrays.jl/src/structarray.jl:100 [inlined]
 [7] #_#7
   @ ~/repos/StructArrays.jl/src/structarray.jl:109 [inlined]
 [8] (StructVector{Foo1, C, I} where {C<:Union{Tuple, NamedTuple}, I})()
   @ StructArrays ~/repos/StructArrays.jl/src/structarray.jl:109
 [9] top-level scope
   @ REPL[56]:1

Reproduce the empty-construction example in Julia, then inspect src/structarray.jl around lines 92, 100, and 109 where StructVector delegates to StructArray. Confirm that the completed behavior is an empty StructVector{Foo1}() without the NamedTuple field error, matching Vector{Foo1}().