fix CurrentItemFilter bug

Author: ukclivecox

server/src/io/seldon/recommendation/filters/base/CurrentItemFilter.java

@@ -26,11 +26,11 @@
 import io.seldon.clustering.recommender.RecommendationContext;
 import io.seldon.recommendation.ItemFilter;
 
-import org.springframework.stereotype.Component;
-
 import java.util.Collections;
 import java.util.List;
 
+import org.springframework.stereotype.Component;
+
 /**
  * Filter for the item that the user is currently interacting with.
  * @author firemanphil
@@ -42,7 +42,10 @@ public class CurrentItemFilter implements ItemFilter {
     @Override
     public List<Long> produceExcludedItems(String client, Long user, String clientUserId, RecommendationContext.OptionsHolder optsHolder,
                                            Long currentItem,String lastRecListUUID, int numRecommendations) {
-        return Collections.singletonList(currentItem);
+    	if (currentItem != null)
+    		return Collections.singletonList(currentItem);
+    	else
+    		return Collections.emptyList();
     }
 }