Scala: How to get default value of parameters using MethodMirror?

I want to use scala reflection to construct a case class from a map. How to fill the parameter list with default value if there is no corresponding key in the input map?

def parser[T: TypeTag: ClassTag](args: Map[String, _]) = {
    val rm = runtimeMirror(classTag[T].runtimeClass.getClassLoader)
    val classSymbol = typeOf[T].typeSymbol.asClass
    val classMirror = rm.reflectClass(classSymbol)
    val constructor = typeOf[T].declaration(nme.CONSTRUCTOR).asMethod
    val constructorMirror = classMirror.reflectConstructor(constructor)

    val constructorArgs = constructor.paramss.flatten.map(param => {
      val paramName = param.name.toString
      if (param.typeSignature <:< typeOf[Option[Any]])
        args.get(paramName)
      else
        args.getOrElse(paramName, "Default Value") //how to get default value here
    })

    constructorMirror(constructorArgs:_*).asInstanceOf[T]
  }

In the above codes, is that possible to get the default value of parameters in the args.getOrElse(paramName, "Default Value")?