pmap error handling fails with batch_size > 1

Here is a MWE

julia> using Distributed

julia> addprocs(2)

julia> pmap(o->error(),zeros(2),on_error= ex->0.0,batch_size=1) # Works as expected
2-element Array{Float64,1}:
 0.0
 0.0

julia> pmap(o->error(),zeros(2),on_error= ex->0.0,batch_size=2) # Fails
ERROR: MethodError: Cannot `convert` an object of type Float64 to an object of type Distributed.BatchProcessingError
Closest candidates are:
  convert(::Type{T}, ::T) where T at essentials.jl:154
  Distributed.BatchProcessingError(::Any, ::Any) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.1/Distributed/src/pmap.jl:4
Stacktrace:
 [1] setindex!(::Array{Distributed.BatchProcessingError,1}, ::Float64, ::Int64) at ./array.jl:767
 [2] process_batch_errors!(::WorkerPool, ::Function, ::Array{Distributed.BatchProcessingError,1}, ::Function, ::Array{Any,1}, ::Nothing) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.1/Distributed/src/pmap.jl:228
 [3] #pmap#213(::Bool, ::Int64, ::Function, ::Array{Any,1}, ::Nothing, ::Function, ::Function, ::WorkerPool, ::Array{Float64,1}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.1/Distributed/src/pmap.jl:148
 [4] (::getfield(Distributed, Symbol("#kw##pmap")))(::NamedTuple{(:on_error, :batch_size),Tuple{getfield(Main, Symbol("##44#46")),Int64}}, ::typeof(pmap), ::Function, ::WorkerPool, ::Array{Float64,1}) at ./none:0
 [5] #pmap#223(::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol},NamedTuple{(:on_error, :batch_size),Tuple{getfield(Main, Symbol("##44#46")),Int64}}}, ::Function, ::Function, ::Array{Float64,1}) at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.1/Distributed/src/pmap.jl:156
 [6] (::getfield(Distributed, Symbol("#kw##pmap")))(::NamedTuple{(:on_error, :batch_size),Tuple{getfield(Main, Symbol("##44#46")),Int64}}, ::typeof(pmap), ::Function, ::Array{Float64,1}) at ./none:0
 [7] top-level scope at none:0

julia> versioninfo()
Julia Version 1.1.1
Commit 55e36cc (2019-05-16 04:10 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin15.6.0)
  CPU: Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 12
  JULIA_EDITOR = nvim

Reproduce the Julia 1.1.1 MWE with Distributed.pmap and compare batch_size=1 with batch_size=2. Start in Distributed/src/pmap.jl at process_batch_errors!, identified in the stack trace; done means on_error returns 0.0 successfully for batch_size=2 without a BatchProcessingError conversion failure.