Handle empty string in System.shell (#13331)

lib/elixir/lib/system.ex

@@ -955,6 +955,12 @@ defmodule System do
   @doc since: "1.12.0"
   @spec shell(binary, keyword) :: {Collectable.t(), exit_status :: non_neg_integer}
   def shell(command, opts \\ []) when is_binary(command) do
+    command |> String.trim() |> do_shell(opts)
+  end
+
+  defp do_shell("", _opts), do: {"", 0}
+
+  defp do_shell(command, opts) do
     assert_no_null_byte!(command, "System.shell/2")
     {close_stdin?, opts} = Keyword.pop(opts, :close_stdin, false)
 

lib/elixir/test/elixir/system_test.exs

@@ -209,6 +209,11 @@ defmodule SystemTest do
       assert {"1\n2\n", 0} = System.shell("x=1; echo $x; echo '2'")
     end
 
+    test "shell/1 with empty string" do
+      assert {"", 0} = System.shell("")
+      assert {"", 0} = System.shell("  ")
+    end
+
     @tag timeout: 1_000
     test "shell/1 returns when command awaits input" do
       assert {"", 0} = System.shell("cat", close_stdin: true)