This PR fixes a bug that can cause a null-pointer exception when visualizing a state transition in a model that has been loaded from a repository.

Background

Consider the following simple state model:

package StateVizTest {
    item def Cmd {
        attribute turnOn : ScalarValues::Boolean;
    }
    state def States {
        entry; then off;
        state off;                                  
        state on;
        transition off_To_on
            first off
            accept cmd : Cmd
                if cmd.turnOn
            then on;
        transition on_To_off
            first on
            accept Cmd
                do action Test
            then off;
    }
}

This would normally be visualized as

However, if the model is published to a repository and then later loaded back into memory rather than being parsed from text, attempting to visualize it results in a null pointer exception.

Normally, the guard expressions and effect actions are rendered using the textual notation from which they were parsed. However, when the model is loaded from a repository, the original textual notation is no longer available. The exception occurs because the code was attampting to call trim() on null text strings.

Code changes

This PR fixes the bug by updating the code in VBehavior.convertToDescription to check if textual notation strings are null before calling trim() on them. After this change, the above model, when loaded from a repository, is visualized without an exception as:

This is probably the best that can be done for now, without re-serializing the text from the abstract syntax or storing the original text as an annotation in the repository.

Note. The lack of rendering of typing on features in the loaded model is due to the featuredType property of FeatureTyping relationships not being set properly for the loaded model. This is not a visualization issue.