address that missing OSID on new sessions is "OK"

* This was a todo and after thinking about it and testing, I do think this is unexpected but OK.
* Any remedy to this should not be happening right here anyway

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalUser/Source/OneSignalUserManagerImpl.swift

@@ -549,9 +549,12 @@ extension OneSignalUserManagerImpl {
         updateSession(sessionCount: 1, sessionTime: nil, refreshDeviceMetadata: true)
 
         // Fetch the user's data if there is a onesignal_id
-        // TODO: What if onesignal_id is missing, because we may init a user from cache but it may be missing onesignal_id. Is this ok.
         if let onesignalId = onesignalId {
             OSUserExecutor.fetchUser(aliasLabel: OS_ONESIGNAL_ID, aliasId: onesignalId, identityModel: user.identityModel, onNewSession: true)
+        } else {
+            // It is possible to init a user from cache who is missing the onesignalId
+            // This can happen if any createUser or identifyUser requests are cached
+            OneSignalLog.onesignalLog(.LL_WARN, message: "OneSignalUserManagerImpl.startNewSession() is unable to fetch user with External ID \(externalId ?? "nil") due to null OneSignal ID")
         }
     }