title: (ArgumentError) expected to: to be given as argument
body: <p>Good day. I have weird <code>ArgumentError</code> in my code even tho the code looks very fine.
  I'm Following the project from <code>Mastering Elixir</code>book.</p>
  <pre><code>defmodule ElixirDrip.Storage.Provider do
    @moduledoc false
  
    @target Application.get_env(:elixir_drip, :storage_provider)
  
  
    defdelegate upload(path, content), to: @target
    defdelegate download(path), to: @target
  end
  </code></pre>
  <p><strong>The error</strong></p>
  <blockquote>
  <p>** (ArgumentError) expected to: to be given as argument</p>
  </blockquote>