OutputChange's target attribute should have a different default value.

The getTarget method of OutputChange attempts to use a default value of "STDERR" for the "target" property when no value has been given, but the "target" property is initialized to the empty string. This causes errors for any parsers that create an OutputChange without explicitly setting the target to something.

I see 3 possible ways to fix this:
1) Initialize the "target" property to null. This is how almost every other change's property works in Liquibase
2) Initializing the "target" property to "STDERR". This is how the message property of StopChange works.
3) Change the "if" statement in getTarget to look for null or the empty string.