Declare the method you need to invoke for the class, or remove the reference to the undefined method.

Noncompliant Code Example

Following code will compile, but on runtime the IsTest method will fail with "METHOD DOES NOT EXIST error" message.

Class Sample.NightWatch Extends %RegisteredObject
{
    Property name As %String;
    Property surname As %String;
    Property age As %Integer;

    ClassMethod FullName() {
      Write !,..name_" "_..surname
    }
}

  ...

Set obj = ##class(Sample.Person).%New()
Set obj.name = "Jon"
Set obj.surname = "Snow"

Do obj.LeaveTheWatch() // METHOD DOES NOT EXIST

Exceptions

All % methods may not be defined, for example system methods.

The usage of short package name is not a bug (%Library.ResultSet can be %ResultSet).

Also %Classes are library classes.