diff --git a/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java b/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java
index df8ea9b..eddd2f4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java
@@ -117,6 +117,11 @@
 
           PatchSet.Id psId = PatchSet.Id.fromRef(e.getRefName());
           PatchSet ps = reviewDb.patchSets().get(psId);
+          if (ps == null) {
+            log.warn("No patch set found for " + u.getRefName());
+            continue;
+          }
+
           final Change change = reviewDb.changes().get(psId.getParentKey());
           if (change == null) {
             log.warn("No change found for " + e.getRefName());