new_contents: from portality.core import app
  
  def argvalidate(caller_name, args_and_rules, exception):
      for anr in args_and_rules:
          arg = anr.get("arg")
          arg_name = anr.get("arg_name")
          inst = anr.get("instance")
          allow_none = anr.get("allow_none", True)
  
          if not allow_none:
              if arg is None:
                  raise exception(caller_name + " expected '" + arg_name + "' not to be None")
  
          if inst is not None and arg is not None:
              if not isinstance(arg, inst):
                  raise exception(caller_name + " expected '" + arg_name + "' to be " + inst.__name__ + " but got " + type(arg).__name__)
  
subject: add library function to validate arguments