Do not format empty lines into line breaks

Author: ak3nji

lib/mix/lib/mix/tasks/format.ex

@@ -544,6 +544,8 @@ defmodule Mix.Tasks.Format do
   defp stdin_or_wildcard("-"), do: [:stdin]
   defp stdin_or_wildcard(path), do: path |> Path.expand() |> Path.wildcard(match_dot: true)
 
+  defp elixir_format("", _formatter_opts), do: ""
+
   defp elixir_format(content, formatter_opts) do
     IO.iodata_to_binary([Code.format_string!(content, formatter_opts), ?\n])
   end