Intermittent NullReferenceException when accessing BusinessNoteStore

[Thomas-Fleming]

I have a service that polls the Evernote every few minutes for updates to a users account. I'm getting an intermittent NullReferenceException on the following line of code:

ENSessionAdvanced.SharedSession.BusinessNoteStore;

StackTrace:

at EvernoteSDK.ENSession.get_IsBusinessUser()
at EvernoteSDK.ENSession.get_BusinessNoteStore()
at EvernoteSDK.Advanced.ENSessionAdvanced.get_BusinessNoteStore()

Catching the exception and trying again soon after seems to continue fine.

[Thomas-Fleming]

Update: This appears to happen under 3 scenarios:

1. The user has exceeded their maximum number of hourly API calls
2. The developer token is invalid
3. Unknown - possibly the business token (the one valid for an hour) has expired and the client tries to access the API before renewing it?