Sprinkler system, hours - number to datetime

Setup, Configuration and Use Items & Sitemaps
6

So the above is working on the Number item. Trying to get the DateTime working but the (last “sendCommand”) fails, tried doing this based on Rich’s type conversions page:

rule "Sprinkler run every hours changed"
when
	Item sprinklerRunEvery changed
then
	val RunEvery = sprinklerRunEvery.state as Number
	val DateTime RunNext = now.plusHours(RunEvery.intValue)

	logInfo("sprinkler", "Updating number item")
	sendCommand(sprinklerNextHour, RunNext.getHourOfDay as Number)

	logInfo("sprinkler", "Updating user friendly datetime item")
	sendCommand(sprinklerNextHourFriendly, DateTimeType.valueOf(RunNext))

end

2018-02-05 13:49:47.812 [ERROR] [ntime.internal.engine.RuleEngineImpl] - Rule 'Sprinkler run every hours changed': An error occurred during the script execution: Could not invoke method: org.eclipse.smarthome.core.library.types.DateTimeType.valueOf(java.lang.String) on instance: null