Use nil for resetting env vars instead of false #4067

Author: José Valim

lib/elixir/lib/system.ex

@@ -493,7 +493,7 @@ defmodule System do
 
   defp validate_env(enum) do
     Enum.map enum, fn
-      {k, false} ->
+      {k, nil} ->
         {String.to_char_list(k), false}
       {k, v} ->
         {String.to_char_list(k), String.to_char_list(v)}

lib/elixir/test/elixir/system_test.exs

@@ -70,7 +70,7 @@ defmodule SystemTest do
 
   test "cmd/3 (with options)" do
     assert {["hello\n"], 0} = System.cmd "echo", ["hello"],
-                                into: [], cd: System.cwd!, env: %{"foo" => "bar", "baz" => false},
+                                into: [], cd: System.cwd!, env: %{"foo" => "bar", "baz" => nil},
                                 arg0: "echo", stderr_to_stdout: true, parallelism: true
   end