JMS selector that tests an undefined attribute does not match any messages -- change in behaviour

Issue

Consider a JMS message that has a property "animal". A selector like this would match and retrieve any messages where "animal" is "dog":

animal='dog'

And, of course, the following would match any message where "animal" was anything other than "dog":

animal<>'dog'

The question arises whether the selector should match messages where the value of "animal" is not set at all. Intuitively it seems that a not-equal selector should match if the attribute is missing; after all, "animal" certainly can't be "dog" if it isn't anything at all. In a sense, the value is null, and null <> 'dog'.

Selectors behaved this way in A-MQ 6.1. In 6.2 and later, however, a selector that tests any undefined attribute will match no messages.