diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/DataStreamAlias.java b/server/src/main/java/org/elasticsearch/cluster/metadata/DataStreamAlias.java
index 598cddd4e8e60..6c045bb09e842 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/DataStreamAlias.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/DataStreamAlias.java
@@ -329,7 +329,7 @@ public String toString() {
             "name='" + name + '\'' +
             ", dataStreams=" + dataStreams +
             ", writeDataStream='" + writeDataStream + '\'' +
-            ", filter=" + filter.string() +
+            ", filter=" + (filter != null ? filter.string() : "null") +
             '}';
     }
 }