fix: Accept nil serializer (#92)

* fix: Accept nil serializer

* Obey the law

---------

Co-authored-by: Mateus Nava <mateus.nava@corp.globo.com>
Co-authored-by: Sami Samhuri <sami@samhuri.net>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### 2.0.1 (Next)
 
+* [#92](https://github.com/ruby-grape/grape-active_model_serializers/pull/92): Fix: accept nil serializer - [@mateusnava](https://github.com/mateusnava).
 * Your contribution here.
 
 ### 2.0.0 (2025/06/02)

lib/grape-active_model_serializers/serializer_resolver.rb

@@ -17,12 +17,14 @@ module Grape
       def serializer_class
         return @serializer_class if defined?(@serializer_class)
 
-        @serializer_class = resource_defined_class
-        @serializer_class ||= collection_class
-        @serializer_class ||= options[:serializer]
-        @serializer_class ||= namespace_inferred_class
-        @serializer_class ||= version_inferred_class
-        @serializer_class ||= resource_serializer_class
+        return nil if options.key?(:serializer) && options[:serializer].nil?
+
+        @serializer_class = resource_defined_class ||
+                            collection_class ||
+                            options[:serializer] ||
+                            namespace_inferred_class ||
+                            version_inferred_class ||
+                            resource_serializer_class
       end
 
       def serializer_options

spec/grape/active_model_serializers/serializer_resolver_spec.rb

@@ -52,6 +52,18 @@ describe Grape::ActiveModelSerializers::SerializerResolver do
         expect(serializer).to be_kind_of(serializer_class)
       end
 
+      context 'specified nil by options' do
+        let(:options) {
+          super().merge(
+            serializer: nil
+          )
+        }
+
+        it 'returns nil' do
+          expect(serializer).to be_nil
+        end
+      end
+
       context 'each serializer' do
         let(:options) {
           super().except(:serializer).merge(