improvement: avoid warning about comparison with nil

the previous implementation was not a security issue because the
actual action would not execute with a `nil` identity

lib/ash_authentication/strategies/magic_link/request_preparation.ex

@@ -26,8 +26,11 @@ defmodule AshAuthentication.Strategy.MagicLink.RequestPreparation do
     identity = Query.get_argument(query, identity_field)
     select_for_senders = Info.authentication_select_for_senders!(query.resource)
 
-    query
-    |> Query.filter(^ref(identity_field) == ^identity)
+    if is_nil(identity) do
+      Query.filter(query, false)
+    else
+      Query.filter(query, ^ref(identity_field) == ^identity)
+    end
     |> Query.before_action(fn query ->
       Ash.Query.ensure_selected(query, select_for_senders)
     end)

lib/ash_authentication/strategies/password/request_password_reset_preparation.ex

@@ -27,8 +27,11 @@ defmodule AshAuthentication.Strategy.Password.RequestPasswordResetPreparation do
       identity = Query.get_argument(query, identity_field)
       select_for_senders = Info.authentication_select_for_senders!(query.resource)
 
-      query
-      |> Query.filter(^ref(identity_field) == ^identity)
+      if is_nil(identity) do
+        Query.filter(query, false)
+      else
+        Query.filter(query, ^ref(identity_field) == ^identity)
+      end
       |> Query.before_action(fn query ->
         Ash.Query.ensure_selected(query, select_for_senders)
       end)