this.caseExpression attribute in CtCase is no longer needed

[algomaster99]

Reference: #4015 (comment)

Before Java 12, only one case expression was allowed per case, so spoon maintained an attribute this.caseExpression which would store the expression corresponding to the case. Java 12 introduced a feature to add multiple expressions to a single case, so this.caseExpressions was introduced, which would contain a list of CtExpressions. The second attribute, this.caseExpressions, made this.caseExpression obsolete.

I propose that we remove the attribute and modify its getters and setters to, instead, return the list's first element and clear the list and insert a single element, respectively. This would reduce redundancy. Another benefit is that some visitors like CtScanner do not even access this.caseExpression. So if someone would have set the case expression using this.setCaseExpression, they won't even see it in their pretty-printed string.

[slarse]

I agree, seems like a good refactoring.

[algomaster99]

I am working on it. I shall submit a PR soon.