diff --git a/IP-learning-graph/src/main/java/cn/ac/iie/service/ingestion/ReadHistoryArangoData.java b/IP-learning-graph/src/main/java/cn/ac/iie/service/ingestion/ReadHistoryArangoData.java
index 5214fc4..94a891d 100644
--- a/IP-learning-graph/src/main/java/cn/ac/iie/service/ingestion/ReadHistoryArangoData.java
+++ b/IP-learning-graph/src/main/java/cn/ac/iie/service/ingestion/ReadHistoryArangoData.java
@@ -97,6 +97,11 @@ public class ReadHistoryArangoData<T extends BaseDocument> extends Thread {
     private void deleteDistinctClientIpByTime(T doc) {
         ArrayList<String> distCip = (ArrayList<String>) doc.getAttribute("DIST_CIP");
         ArrayList<Long> distCipTs = (ArrayList<Long>) doc.getAttribute("DIST_CIP_TS");
+        if (distCip == null || distCip.isEmpty()){
+            doc.updateAttribute("DIST_CIP", new String[0]);
+            doc.updateAttribute("DIST_CIP_TS", new long[0]);
+            return;
+        }
         distCipTs.add(currentHour - RECENT_COUNT_HOUR * 3600);
         Collections.sort(distCipTs);
         Collections.reverse(distCipTs);