Reinforcing test on empty models

src/main/java/cli/Action.java

src/main/java/cli/Interpreter.java

src/main/java/cli/Print.java

src/main/java/ui/MainGUI.java

ttool/src/test/java/cli/CLIModelTest.java

ttool/src/test/resources/cli/input/scriptemptymodel

ttool/src/test/resources/cli/input/scriptmodel