From 919597df7c49bb9d18835123970d27e9653f2876 Mon Sep 17 00:00:00 2001
From: pnezis <pnezis@gmail.com>
Date: Wed, 11 Mar 2026 18:01:39 +0200
Subject: [PATCH] Fix invalid mfa validation if value was `nil`

---
 lib/nimble_options.ex        |  2 +-
 test/nimble_options_test.exs | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/nimble_options.ex b/lib/nimble_options.ex
index a26fd60..71f2bef 100644
--- a/lib/nimble_options.ex
+++ b/lib/nimble_options.ex
@@ -700,7 +700,7 @@ defmodule NimbleOptions do
     {:ok, value}
   end
 
-  defp validate_type(:mfa, key, value, redact) when not is_nil(value) do
+  defp validate_type(:mfa, key, value, redact) do
     structured_error_tuple(key, value, "tuple {mod, fun, args}", inspect(value), redact)
   end
 
diff --git a/test/nimble_options_test.exs b/test/nimble_options_test.exs
index 39d319b..cab96bc 100644
--- a/test/nimble_options_test.exs
+++ b/test/nimble_options_test.exs
@@ -666,6 +666,22 @@ defmodule NimbleOptionsTest do
              }
     end
 
+    test "mfa rejects nil" do
+      schema = [transformer: [type: :mfa]]
+
+      opts = [transformer: nil]
+
+      assert NimbleOptions.validate(opts, schema) == {
+               :error,
+               %ValidationError{
+                 key: :transformer,
+                 value: nil,
+                 message:
+                   "invalid value for :transformer option: expected tuple {mod, fun, args}, got: nil"
+               }
+             }
+    end
+
     test "redacted invalid mfa" do
       schema = [transformer: [type: :mfa, redact: true]]