fix: check for nil before expanding path

lib/avrora/client.ex

@@ -129,7 +129,11 @@ defmodule Avrora.Client do
           else
             def self, do: get(@opts, :config, __MODULE__)
             def schemas_path, do: Application.app_dir(@otp_app, get(@opts, :schemas_path, "./priv/schemas"))
-            def registry_ssl_cacert_path, do: Path.expand(get(@opts, :registry_ssl_cacert_path, nil))
+            def registry_ssl_cacert_path do
+              if path = get(@opts, :registry_ssl_cacert_path, nil) do
+                Path.expand(path)
+              end
+            end
 
             defp get(opts, key, default) do
               app_opts = Application.get_env(@otp_app, unquote(:"Elixir.#{module}"), [])

test/avrora/client_test.exs

@@ -61,5 +61,9 @@ defmodule Avrora.ClientTest do
 
       assert Beta.Config.names_cache_ttl() == :infinity
     end
+
+    test "when otp_app is set and registry_ssl_cacert_path is not set" do
+      assert Gamma.Config.registry_ssl_cacert_path == nil
+    end
   end
 end