diff --git a/server/src/internalClusterTest/java/org/opensearch/nodestats/NodeStatsIT.java b/server/src/internalClusterTest/java/org/opensearch/nodestats/NodeStatsIT.java
index cf40b73d5178d..b2c834a10a13d 100644
--- a/server/src/internalClusterTest/java/org/opensearch/nodestats/NodeStatsIT.java
+++ b/server/src/internalClusterTest/java/org/opensearch/nodestats/NodeStatsIT.java
@@ -399,7 +399,6 @@ public void testNodeIndicesStatsXContentWithAggregationOnNodes() {
         testLevels.add(MockStatsLevel.NODE);
         testLevels.add(MockStatsLevel.INDICES);
         testLevels.add(MockStatsLevel.SHARDS);
-        testLevels.add(MockStatsLevel.UNKNOWN);
 
         internalCluster().startNode();
         ensureGreen();
@@ -431,7 +430,7 @@ public void testNodeIndicesStatsXContentWithAggregationOnNodes() {
 
                 builder.startObject();
 
-                if (!testLevel.equals(MockStatsLevel.SHARDS)){
+                if (!testLevel.equals(MockStatsLevel.SHARDS)) {
                     final XContentBuilder failedBuilder = builder;
                     assertThrows(
                         "Expected shard stats in response for generating [SHARDS] field",
@@ -439,7 +438,9 @@ public void testNodeIndicesStatsXContentWithAggregationOnNodes() {
                         () -> nodeStats.getIndices()
                             .toXContent(
                                 failedBuilder,
-                                new ToXContent.MapParams(Collections.singletonMap("level", NodeIndicesStats.StatsLevel.SHARDS.getRestName()))
+                                new ToXContent.MapParams(
+                                    Collections.singletonMap("level", NodeIndicesStats.StatsLevel.SHARDS.getRestName())
+                                )
                             )
                     );
                 } else {
@@ -470,7 +471,9 @@ public void testNodeIndicesStatsXContentWithAggregationOnNodes() {
                         () -> nodeStats.getIndices()
                             .toXContent(
                                 failedBuilder,
-                                new ToXContent.MapParams(Collections.singletonMap("level", NodeIndicesStats.StatsLevel.INDICES.getRestName()))
+                                new ToXContent.MapParams(
+                                    Collections.singletonMap("level", NodeIndicesStats.StatsLevel.INDICES.getRestName())
+                                )
                             )
                     );
                 } else {
@@ -500,6 +503,42 @@ public void testNodeIndicesStatsXContentWithAggregationOnNodes() {
         });
     }
 
+    public void testNodeIndicesStatsUnknownLevelThrowsException() {
+        List<MockStatsLevel> testLevels = new ArrayList<>();
+
+        testLevels.add(MockStatsLevel.UNKNOWN);
+        internalCluster().startNode();
+        ensureGreen();
+        String indexName = "test1";
+        assertAcked(
+            prepareCreate(
+                indexName,
+                clusterService().state().getNodes().getSize(),
+                Settings.builder().put("number_of_shards", 2).put("number_of_replicas", clusterService().state().getNodes().getSize() - 1)
+            )
+        );
+        ensureGreen();
+
+        testLevels.forEach(testLevel -> {
+            NodesStatsResponse response;
+            CommonStatsFlags commonStatsFlags = new CommonStatsFlags();
+            commonStatsFlags.setIncludeIndicesStatsByLevel(true);
+            if (!testLevel.equals(MockStatsLevel.NULL)) {
+                ArrayList<String> level_arg = new ArrayList<>();
+                level_arg.add(testLevel.getRestName());
+
+                commonStatsFlags.setLevels(level_arg.toArray(new String[0]));
+            }
+            response = client().admin().cluster().prepareNodesStats().setIndices(commonStatsFlags).get();
+
+            assertTrue(response.hasFailures());
+            assertEquals(
+                "Level provided is not supported by NodeIndicesStats",
+                response.failures().get(0).getCause().getCause().getMessage()
+            );
+        });
+    }
+
     private Map<String, Object> xContentBuilderToMap(XContentBuilder xContentBuilder) {
         return XContentHelper.convertToMap(BytesReference.bytes(xContentBuilder), true, xContentBuilder.contentType()).v2();
     }
diff --git a/server/src/main/java/org/opensearch/indices/NodeIndicesStats.java b/server/src/main/java/org/opensearch/indices/NodeIndicesStats.java
index ad786d236f3ce..4a5e216b514ae 100644
--- a/server/src/main/java/org/opensearch/indices/NodeIndicesStats.java
+++ b/server/src/main/java/org/opensearch/indices/NodeIndicesStats.java
@@ -61,17 +61,14 @@
 import org.opensearch.index.translog.TranslogStats;
 import org.opensearch.index.warmer.WarmerStats;
 import org.opensearch.search.suggest.completion.CompletionStats;
-import org.opensearch.transport.TransportException;
 
 import java.io.IOException;
-import java.rmi.UnexpectedException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import java.util.stream.Collectors;
 
 /**
  * Global information on indices stats running on a specific node.
@@ -171,7 +168,7 @@ private static StatsLevel getAcceptedLevel(String[] levels) {
             Optional<StatsLevel> level = Arrays.stream(StatsLevel.values())
                 .filter(field -> field.getRestName().equals(levels[0]))
                 .findFirst();
-            return level.orElse(null);
+            return level.orElseThrow(() -> new IllegalArgumentException("Level provided is not supported by NodeIndicesStats"));
         }
         return null;
     }
@@ -344,7 +341,9 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         stats.toXContent(builder, params);
 
         if (StatsLevel.INDICES.getRestName().equals(level)) {
-            assert statsByIndex!=null || statsByShard!=null: "Expected shard stats or index stats in response for generating [" + StatsLevel.INDICES + "] field";
+            assert statsByIndex != null || statsByShard != null : "Expected shard stats or index stats in response for generating ["
+                + StatsLevel.INDICES
+                + "] field";
             if (statsByIndex == null) {
                 statsByIndex = createStatsByIndex(statsByShard);
             }
@@ -360,7 +359,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
             builder.endObject();
         } else if (StatsLevel.SHARDS.getRestName().equals(level)) {
             builder.startObject(StatsLevel.SHARDS.getRestName());
-            assert statsByShard != null: "Expected shard stats in response for generating [" + StatsLevel.SHARDS + "] field";
+            assert statsByShard != null : "Expected shard stats in response for generating [" + StatsLevel.SHARDS + "] field";
             for (Map.Entry<Index, List<IndexShardStats>> entry : statsByShard.entrySet()) {
                 builder.startArray(entry.getKey().getName());
                 for (IndexShardStats indexShardStats : entry.getValue()) {