Virtual fields in batch not included in graph's metadata

[fishtreesugar]

reproduce:

Mix.install([
  {:pacer, "~> 0.1.6"}
])

defmodule Foo do
  use Pacer.Workflow

  graph do
    field(:foo, virtual?: true)
    batch :bar do
      field(:baz, resolver: &__MODULE__.one/1, default: nil, virtual?: true)
      field(:quux, resolver: &__MODULE__.one/1, default: nil, virtual?: true)
    end
  end

  def one(_), do: 1
end

 [:foo] = Foo.__graph__(:virtual_fields) # matched
 [:foo, :baz, :quux] = Foo.__graph__(:virtual_fields) # MatchError