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 c5360c8..5b39824 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/reviewersbyblame/RefUpdateListener.java
@@ -98,6 +98,10 @@
           PatchSet.Id psId = PatchSet.Id.fromRef(u.getRefName());
           PatchSet ps = reviewDb.patchSets().get(psId);
           final Change change = reviewDb.changes().get(psId.getParentKey());
+          if (change == null) {
+            log.warn("No change found for " + u.getRefName());
+            continue;
+          }
 
           final RevCommit commit =
               rw.parseCommit(ObjectId.fromString(u.getNewObjectId()));