Change mix format to skip empty .ex and .exs files

Author: ak3nji

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

@@ -561,7 +561,7 @@ defmodule Mix.Tasks.Format do
 
   defp format_file({file, formatter}, task_opts) do
     input = read_file(file)
-    output = formatter.(input)
+    output = (bit_size(input) > 0 && formatter.(input)) || <<>>
     check_formatted? = Keyword.get(task_opts, :check_formatted, false)
     dry_run? = Keyword.get(task_opts, :dry_run, false)