fix: add [] as fallback for modules = Application.spec(app, :modules) (ash-project#2620)

Author: Torkan

lib/ash/info.ex

@@ -77,7 +77,7 @@ defmodule Ash.Info do
   """
   @spec defined_extensions(app :: Application.app()) :: [module()]
   def defined_extensions(app) do
-    modules = Application.spec(app, :modules)
+    modules = Application.spec(app, :modules) || []
     # Preload the modules to improve performance.
     Code.ensure_all_loaded(modules)
     Enum.filter(modules, &Spark.implements_behaviour?(&1, Spark.Dsl.Extension))