Ensure matching escapes for nil and empty strings

Closes #444.

Author: josevalim

lib/phoenix_html/engine.ex

@@ -16,6 +16,7 @@ defmodule Phoenix.HTML.Engine do
   """
   def encode_to_iodata!({:safe, body}), do: body
   def encode_to_iodata!(nil), do: ""
+  def encode_to_iodata!(""), do: ""
   def encode_to_iodata!(bin) when is_binary(bin), do: html_escape(bin)
   def encode_to_iodata!(list) when is_list(list), do: Phoenix.HTML.Safe.List.to_iodata(list)
   def encode_to_iodata!(other), do: Phoenix.HTML.Safe.to_iodata(other)

test/phoenix_html_test.exs

@@ -36,6 +36,12 @@ defmodule Phoenix.HTMLTest do
         html_escape(~c"foo🐥")
       end
     end
+
+    test "equivalences" do
+      # Since some HTML code may compare html_escape("") with html_escape(nil),
+      # we make sure they have equivalent representations.
+      assert html_escape("") == html_escape(nil)
+    end
   end
 
   describe "attributes_escape" do