fix: Accept nil serializer

Author: Mateus Nava

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### 1.5.3 (Next)
 
 * Your contribution here.
+* [#92](https://github.com/ruby-grape/grape-active_model_serializers/pull/92): Fix: accept nil serializer - [@mateusnava](https://github.com/mateusnava).
 
 ### 1.5.2 (March 14, 2018)
 

lib/grape-active_model_serializers/serializer_resolver.rb

@@ -16,6 +16,9 @@ def serializer
 
       def serializer_class
         return @serializer_class if defined?(@serializer_class)
+
+        return nil if options.key?(:serializer) && options[:serializer].nil?
+
         @serializer_class = resource_defined_class
         @serializer_class ||= collection_class
         @serializer_class ||= options[:serializer]

spec/grape/active_model_serializers/serializer_resolver_spec.rb

@@ -52,6 +52,18 @@
         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(