presto-parser/src/main/java/io/prestosql/sql/ExpressionFormatter.java/Formatter/visitWhenClause
class Formatter:        @Override
        protected String visitWhenClause(WhenClause node, Void context)
        {
            return "WHEN " + process(node.getOperand(), context) + " THEN " + process(node.getResult(), context);
        }