code: def normalize_item(item, field_def)
        return case field_def[:type]
          when 'long', 'int' then Integer(item)
          when 'double', 'float' then Float(item)
          when 'boolean' then item.kind_of?(String) ?
              item.casecmp('true') == 0 : item
          else item
        end
      end
docs: Converts one leaf item to a built-in type.