presto-main/src/main/java/io/prestosql/type/UnknownOperators.java/UnknownOperators/indeterminate
class UnknownOperators:    @ScalarOperator(INDETERMINATE)
    @SqlType(StandardTypes.BOOLEAN)
    public static boolean indeterminate(@SqlType("unknown") @SqlNullable Boolean value)
    {
        return true;
    }