Domain object toString null check

Question

Following advice to "Make good use of toString() for all Domain classes", I made what I thought was the most useful toString for my class. I found that certain operations happen before there are values for the components of the toString. I wonder if there is a cleaner way to check for nulls or even if I need to approach things differently. As I'm writing, it occurs to me that depending on other objects in a toString is probably a bad idea.

class AssessmentStep {
    String hours
    Date assStepDate
    Assessment ass
    Step step
    Integer assStepProgress
    static hasMany =[stepNotes:StepNote]

    @Override
    String toString(){
        String stepString = "null"
        String appString = ""
        if (step != null && step.stepName != null){
            stepString = step.stepName
        }
        if (ass !=null && ass.app != null && ass.app.appName != null){
            appString = ass.app.appName
        }

        return appString + " " + stepString
    }

Answer 1

You could do:

String toString(){
    "${ass?.app?.appName ?: ''} ${step?.stepName ?: 'null'}"
}

Answer 2

You could also do the following...

[ass?.app?.appName, step?.stepName].minus(null).join(" ")

This creates a List containing the two values, removes any null values from the List, and then builds a string separating the values with a space character (i.e. the join).