diff --git a/x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/SyntheticSourceIndexSettingsProvider.java b/x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/SyntheticSourceIndexSettingsProvider.java
index 59c4d96cd88bc..dc9df452db36d 100644
--- a/x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/SyntheticSourceIndexSettingsProvider.java
+++ b/x-pack/plugin/logsdb/src/main/java/org/elasticsearch/xpack/logsdb/SyntheticSourceIndexSettingsProvider.java
@@ -100,6 +100,7 @@ boolean newIndexHasSyntheticSourceUsage(
         tmpIndexMetadata.settings(finalResolvedSettings);
         // Create MapperService just to extract keyword dimension fields:
         try (var mapperService = mapperServiceFactory.apply(tmpIndexMetadata.build())) {
+            // combinedTemplateMappings can be null when creating system indices
             if (combinedTemplateMappings == null || combinedTemplateMappings.isEmpty()) {
                 // this can happen when creating a normal index that doesn't match any template and without mapping.
                 combinedTemplateMappings = List.of(new CompressedXContent("{}"));