Ok now I know what it does, I have overseen the not empty thing...
java.lang.IllegalStateException: Impossible coverage requirements, defined steps [] not found.
at osmo.tester.generator.endcondition.structure.StepCoverage.init(StepCoverage.java:109)
at osmo.tester.generator.MainGenerator.beforeTest(MainGenerator.java:335)
at osmo.tester.generator.MainGenerator.nextTest(MainGenerator.java:104)
at osmo.tester.generator.MainGenerator.generate(MainGenerator.java:70)
the list has an empty string... sorry :D