Subscription service: fix create monitored item returning unexpected Bad_OutOfMemory item status
Description
Create monitored item returns unexpected Bad_OutOfMemory status code for items.
Analysis
Create Monitored Item service returned Bad_OutOfMemory status for items in case of error of BadUserAccessDenied, BadNotReadable or BadIndexRangeInvalid cases in which the MontioredItem shall be created and the status shall be returned in first notification. This was due to a bug in C code adding fist monitored item notification, the value was expected to never be NULL whereas it is the case when the status code is not Good.
Fix
Change B model to indicate value can be NULL and change C code to accept NULL value as a valid input if status != Good.