Fix bwc for cluster manager throttling settings (opensearch-project#5305)

Signed-off-by: Dhwanil Patel <[email protected]>

Author: dhwanilpatel

server/src/main/java/org/opensearch/cluster/service/ClusterManagerTaskThrottler.java

@@ -108,10 +108,12 @@ public boolean isThrottlingEnabled() {
     }
 
     void validateSetting(final Settings settings) {
-        if (minNodeVersionSupplier.get().compareTo(Version.V_2_4_0) < 0) {
-            throw new IllegalArgumentException("All the nodes in cluster should be on version later than or equal to 2.4.0");
-        }
         Map<String, Settings> groups = settings.getAsGroups();
+        if (groups.size() > 0) {
+            if (minNodeVersionSupplier.get().compareTo(Version.V_2_4_0) < 0) {
+                throw new IllegalArgumentException("All the nodes in cluster should be on version later than or equal to 2.4.0");
+            }
+        }
         for (String key : groups.keySet()) {
             if (!THROTTLING_TASK_KEYS.containsKey(key)) {
                 throw new IllegalArgumentException("Cluster manager task throttling is not configured for given task type: " + key);

server/src/test/java/org/opensearch/cluster/service/ClusterManagerTaskThrottlerTests.java

@@ -114,6 +114,15 @@ public void testValidateSettingsForDifferentVersion() {
 
         Settings newSettings = Settings.builder().put("cluster_manager.throttling.thresholds.put-mapping.value", newLimit).build();
         assertThrows(IllegalArgumentException.class, () -> throttler.validateSetting(newSettings));
+
+        // validate for empty setting, it shouldn't throw exception
+        Settings emptySettings = Settings.builder().build();
+        try {
+            throttler.validateSetting(emptySettings);
+        } catch (Exception e) {
+            // it shouldn't throw exception
+            throw new AssertionError(e);
+        }
     }
 
     public void testValidateSettingsForTaskWihtoutRetryOnDataNode() {