empty covered by not equals - not allowed

test/fun_core/basic_signup_whitelist_test.exs

@@ -9,6 +9,10 @@ defmodule FunCore.BasicSignupWhitelistTest do
     refute(mail_whitelisted_fun(nil, "joe@example.com"))
   end
 
+  test "When empty, not whitelisted" do
+    refute(mail_whitelisted_fun("", "joe@example.com"))
+  end
+
   test "When set and mach, then whitelisted" do
     assert(mail_whitelisted_fun("joe@example.com", "joe@example.com"))
   end