fix null case

Author: sebapastore

packages/core/lib/plugins/segment_destination.dart

@@ -35,7 +35,7 @@ class SegmentDestination extends DestinationPlugin with Flushable {
         final succeeded = await analytics?.httpClient.startBatchUpload(
             analytics!.state.configuration.state.writeKey, batch,
             host: _apiHost);
-        if (succeeded) {
+        if (succeeded == true) {
           sentEvents.addAll(batch);
         } else {
           numFailedEvents += batch.length;