def transform_value(value, transform)
      case transform
      when nil
        value
      when Proc
        @parent.instance_exec(value, &transform)
      when Symbol
        value.public_send(transform)
      end
    end
def transform_value(value, transform)
      case transform
      when nil
        value
      when Proc
        @parent.instance_exec(value, &transform)
      when Symbol
        value.public_send(transform)
      end
    end
Apply a transformation to a value.
 @param value [Object] a value
 @param transform [nil, Proc, Symbol] a transform type
 @return [Object] the transformed value