Cannot map day of week (5#1)

[alexey-anufriev]

It is not possible to perform the following mapping:

CronDefinition cronDefinition = CronDefinitionBuilder.instanceDefinitionFor(CronType.SPRING);
CronParser cronParser = new CronParser(cronDefinition);
Cron cron = cronParser.parse("0 0 0 ? * 5#1");
CronMapper mapper = CronMapper.fromSpringToQuartz();
Cron quartzCron = mapper.map(cron);

Execution leads to the following exception:

java.lang.IllegalArgumentException: value missing for a#b cron expression

	at com.cronutils.utils.Preconditions.checkArgument(Preconditions.java:110)
	at com.cronutils.model.field.expression.On.<init>(On.java:43)
	at com.cronutils.mapper.CronMapper$1.visit(CronMapper.java:294)
	at com.cronutils.model.field.expression.On.accept(On.java:70)
	at com.cronutils.mapper.CronMapper.lambda$dayOfWeekMapping$5(CronMapper.java:288)
	at com.cronutils.mapper.CronMapper.map(CronMapper.java:88)

[jmrozanec]

@alexey-anufriev may we ask you for a PR with the corresponding test? Thanks!

[alexey-anufriev]

Sure, #606