Elixir: Parsing initials of a given name

iex

iex(2)> c "name.ex"
[Name]
iex(3)> Name.initials("Cher")
"C"
iex(4)> Name.initials("Barry Bluejeans")
"BB"
iex(5)> Name.initials("Jean-Claude Van Damme")
"JVD"

name.ex

defmodule Name do
  def initials(name) when name in [nil, ""], do: "?"

  def initials(name) when is_binary(name) do
    name
    |> String.split(" ")
    |> extract_initials()
  end

  defp extract_initials([]), do: ""
  defp extract_initials([name_part | name_parts]) do
    String.slice(name_part, 0, 1) <> extract_initials(name_parts)
  end
end