Handling null entries

[rob42]

Placeholder to remind to attend to null writes and consequent reads.

When we have full history we cant just drop the key from a map or such, as we will then get the last valid value, which will be wrong. So we must write a null entry, which we do.

Assume we have set a notification eg
notifications.environment.depth.belowKeel.values.nmea1.II.value.state=alarm

When we have a null object value (alarm ended) being set the influxdbService writes the value as null, eg notifications.environment.depth.belowKeel.values.nmea1.II.value=null,

however this leaves the objects attributes set, eg notifications.environment.depth.belowKeel.values.nmea1.II.value.state=alarm as this is a separate influx key.

Alternatively if we set the notification with null attributes we get the attributes as null (good) but the notification will still be an object of null attributes. (bad)

Need a good way to have both value nullify attributes without a lot of overhead as its not a common case.