DefaultDict accessor fails when the default is not the value type

MWE:

pkg> st DataStructures
  [864edb3b] DataStructures v0.18.18

julia> using DataStructures

julia> dd = DefaultDict(1, :a => (2,))
DefaultDict{Symbol, Tuple{Int64}, Int64} with 1 entry:
  :a => (2,)

julia> dd[:b]
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Tuple{Int64}

Closest candidates are:
  convert(::Type{T}, ::T) where T<:Tuple
   @ Base essentials.jl:451
  convert(::Type{T}, ::T) where T
   @ Base Base.jl:84
  convert(::Type{T}, ::CartesianIndex) where T<:Tuple
   @ Base multidimensional.jl:136
  ...

Stacktrace:
 [1] get!
   @ Base ./dict.jl:481 [inlined]
 [2] get!
   @ Base ./abstractdict.jl:552 [inlined]
 [3] getindex
   @ DataStructures ~/.julia/packages/DataStructures/jFDPC/src/default_dict.jl:63 [inlined]
 [4] getindex(a::DefaultDict{Symbol, Tuple{Int64}, Int64}, args::Symbol)
   @ DataStructures ~/.julia/packages/DataStructures/jFDPC/src/delegate.jl:21
 [5] top-level scope
   @ REPL[111]:1

Reproduce the MWE in the Julia REPL, then inspect src/default_dict.jl at the getindex location and the delegation in src/delegate.jl. Trace how the default is passed to get!, determine the intended behavior for mismatched default and value types, and verify the reported MethodError is resolved with regression coverage.