FIX: use safe navigation operator for params (#177)

* FIX: use safe navigation operator for params

Bug report: https://meta.discourse.org/t/-/289850
Solution ref: https://stackoverflow.com/questions/34794697

* added spec

* formatting fix

lib/discourse_topic_voting/categories_controller_extension.rb

@@ -4,7 +4,7 @@ module DiscourseTopicVoting
   module CategoriesControllerExtension
     def category_params
       @vote_enabled ||=
-        !!ActiveRecord::Type::Boolean.new.cast(params[:custom_fields][:enable_topic_voting])
+        !!ActiveRecord::Type::Boolean.new.cast(params&.[](:custom_fields)&.[](:enable_topic_voting))
 
       category_params = super
 

spec/requests/categories_controller_spec.rb

@@ -44,4 +44,9 @@
         }
     expect(Category.can_vote?(category.id)).to eq(false)
   end
+
+  it "works fine when `custom_fields` isn't passed " do
+    put "/categories/#{category.id}.json", params: { hello: "world" }
+    expect(response.status).to eq(200)
+  end
 end