instance method fetch

# File activemodel/lib/active_model/indexed_row.rb, line 173
      def fetch(column)
        if index = @indexes[column]
          value = @row[index]
          if UNSET.equal?(value)
            if block_given?
              yield
            else
              raise KeyError, "key not found: #{column.inspect}"
            end
          else
            value
          end
        elsif block_given?
          yield
        else
          raise KeyError, "key not found: #{column.inspect}"
        end
      end