use fetch rather than both Hash#key? and Hash#[]

activerecord/lib/active_record/attribute_methods/read.rb

@@ -92,12 +92,14 @@ def cacheable_column?(column)
         end
 
         def internal_attribute_access_code(attr_name, cast_code)
-            access_code = "(v=@attributes[attr_name]) && #{cast_code}"
-
-            unless attr_name == primary_key
-              access_code.insert(0, "missing_attribute(attr_name, caller) unless @attributes.has_key?(attr_name); ")
+          if attr_name == primary_key
+            access_code = "v = @attributes[attr_name];"
+          else
+            access_code = "v = @attributes.fetch(attr_name) { missing_attribute(attr_name, caller) };"
           end
 
+          access_code << "v && #{cast_code};"
+
           if cache_attribute?(attr_name)
             access_code = "@attributes_cache[attr_name] ||= (#{access_code})"
           end