diff --git a/java/com/google/gerrit/server/git/ChangesByProjectCacheImpl.java b/java/com/google/gerrit/server/git/ChangesByProjectCacheImpl.java
index b5a53b2..66c63c6 100644
--- a/java/com/google/gerrit/server/git/ChangesByProjectCacheImpl.java
+++ b/java/com/google/gerrit/server/git/ChangesByProjectCacheImpl.java
@@ -286,7 +286,7 @@
       int size = 0;
       size += JavaWeights.OBJECT; // change
       size += JavaWeights.REFERENCE + GerritWeights.KEY_INT; // changeId
-      size += JavaWeights.REFERENCE + c.getServerId().length();
+      size += JavaWeights.REFERENCE + (c.getServerId() == null ? 0 : c.getServerId().length());
       size += JavaWeights.REFERENCE + JavaWeights.OBJECT + 40; // changeKey;
       size += JavaWeights.REFERENCE + GerritWeights.TIMESTAMP; // createdOn;
       size += JavaWeights.REFERENCE + GerritWeights.TIMESTAMP; // lastUpdatedOn;