This inspection reports on subclasses of java.lang.Comparator which are not
also Serializable. Objects of java.util.TreeMap
or java.util.TreeSet will become non-Serializable
if instantated with such Comparators. This can result in unexpected and difficult-to-diagnose
bugs. Since subclasses of java.lang.Comparator are often stateless, simply marking
them Serializable is a small cost to avoid such issues.