presto-spi/src/main/java/io/prestosql/spi/predicate/EquatableValueSet.java/EquatableValueSet/getSingleValue
class EquatableValueSet:    @Override
    public Object getSingleValue()
    {
        if (!isSingleValue()) {
            throw new IllegalStateException("EquatableValueSet does not have just a single value");
        }
        return entries.iterator().next().getValue();
    }