Update tidy_raw() to ignore null values

lib/outlook_web/view_helpers.ex

@@ -3,10 +3,13 @@ defmodule OutlookWeb.ViewHelpers do
   import Phoenix.HTML, only: [raw: 1]
 
   @doc "Just sanitize tags"
-  def tidy_raw(html) do
+  def tidy_raw(html) when is_binary(html) do
     html
     |> Floki.parse_fragment!()
     |> Floki.raw_html()
     |> raw
   end
+  def tidy_raw(whatever) do
+    whatever
+  end
 end