Use time-based subscription position in CatchupSubscriptionModel if i…

…t's not possible to get the global position from MongoDB

subscription/util/blocking/catchup-subscription/src/main/java/org/occurrent/subscription/blocking/durable/catchup/CatchupSubscriptionModel.java

@@ -135,7 +135,8 @@ public Subscription subscribe(String subscriptionId, SubscriptionFilter filter,
         // Here's the reason why we're forcing the wrapping subscription to be a PositionAwareBlockingSubscription.
         // This is in order to be 100% safe since we need to take events that are published meanwhile the EventStoreQuery
         // is executed. Thus, we need the global position of the subscription at the time of starting the query.
-        SubscriptionPosition globalSubscriptionPosition = subscriptionModel.globalSubscriptionPosition();
+        SubscriptionPosition globalSubscriptionPositionFromSubscriptionModel = subscriptionModel.globalSubscriptionPosition();
+        SubscriptionPosition globalSubscriptionPosition = Objects.requireNonNullElseGet(globalSubscriptionPositionFromSubscriptionModel, () -> new TimeBasedSubscriptionPosition(OffsetDateTime.now()));
 
         FixedSizeCache cache = new FixedSizeCache(config.cacheSize);
         final Stream<CloudEvent> stream;
@@ -180,14 +181,11 @@ public Subscription subscribe(String subscriptionId, SubscriptionFilter filter,
                     // (i.e. written by the catch-up subscription), we save the globalSubscriptionPosition.
                     // The reason that we need to write the time-based subscription position in this case
                     // is that the wrapped subscription might not support time-based subscriptions.
-                    if ((position == null || isTimeBasedSubscriptionPosition(position)) && globalSubscriptionPosition != null) {
+                    if (position == null || isTimeBasedSubscriptionPosition(position)) {
                         position = cfg.storage().save(subscriptionId, globalSubscriptionPosition);
-                    } else if (position == null) {
-                        // Position can still be null here if globalSubscriptionPosition is null, if so, we start at the "subscriptionModelDefault"
-                        return StartAt.subscriptionModelDefault();
                     }
                     return StartAt.subscriptionPosition(position);
-                }).orElse(() -> globalSubscriptionPosition == null ? StartAt.subscriptionModelDefault() : StartAt.subscriptionPosition(globalSubscriptionPosition)));
+                }).orElse(() -> StartAt.subscriptionPosition(globalSubscriptionPosition)));
 
         final Subscription subscription;
         if (subscriptionsWasCancelledOrShutdown) {