Unwieldy nil checks in Elixir

account.ex

defmodule Account do
  # Unwieldy nil checks
  def display_name(%{first: nil, last: nil, username: nil}) do
    display_name(%{})
  end
  def display_name(%{first: nil, last: nil, username: username}) do
    display_name(%{username: username})
  end
  def display_name(%{first: nil, last: nil}), do: display_name(%{})

  # Happy paths
  def display_name(%{first: first, last: last}) do
    do_trim("#{first} #{last}")
  end
  def display_name(%{username: username}), do: "#{username}"
  def display_name(_), do: "New User"
end