presto-main/src/main/java/io/prestosql/sql/planner/iterative/RuleIndex.java/RuleIndex/RuleIndex
class RuleIndex:    private RuleIndex(ListMultimap<Class<?>, Rule<?>> rulesByRootType)
    {
        this.rulesByRootType = ImmutableListMultimap.copyOf(rulesByRootType);
    }