Copy Formtastic 2.1.1's #input_class in case user has Formtastic 2.2

Author: James McKinney

lib/active_admin/form_builder.rb

@@ -125,6 +125,14 @@ def active_admin_input_class_name(as)
       "ActiveAdmin::Inputs::#{as.to_s.camelize}Input"
     end
 
+    # Copy Formtastic 2.1.1's #input_class in case user has Formtastic 2.2
+    def input_class(as)
+      @input_classes_cache ||= {}
+      @input_classes_cache[as] ||= begin
+        Rails.application.config.cache_classes ? input_class_with_const_defined(as) : input_class_by_trying(as)
+      end
+    end
+
     # prevent exceptions in production environment for better performance
     def input_class_with_const_defined(as)
       input_class_name = custom_input_class_name(as)