Case file conditional event fails other cases

It is not possible to start a case without setting case file data when another case definition within the same kjar has conditional event expression using some data from the Case File.

To best describe the problem - see the reproducer [1] which only adds new case definition with conditional event which awaits for case file documents. Though other cases in the kjar doesn't need this particular Case File documents variable, the original tests fail (but shouldn't) as they are influenced by the exception Error evaluating constraint '((java.util.List)data.get("Documents")).size() > 0' in [Rule "RuleFlowStateNode-CaseFileConditionalEvent-2-3-DROOLS_DEFAULT"

[1] Reproducer - the tests start failing - Tests run: 45, Failures: 0, Errors: 24, Skipped: 0
https://github.com/droolsjbpm/jbpm/pull/723