code refactor not to occur nullpointer exception (#2816)

Signed-off-by: Dhrubo Saha <[email protected]>
(cherry picked from commit a4dff63)

Author: dhrubo-os

plugin/src/main/java/org/opensearch/ml/model/MLModelManager.java

@@ -925,7 +925,7 @@ private void deleteOrUpdateModelGroup(String modelGroupID, Boolean doesVersionCr
         // This checks if model group is created when registering the version. If yes,
         // model group is deleted since the version registration
         // had failed. Else model group latest version is decremented by 1
-        if (doesVersionCreateModelGroup) {
+        if (Boolean.TRUE.equals(doesVersionCreateModelGroup)) {
             DeleteRequest deleteModelGroupRequest = new DeleteRequest();
             deleteModelGroupRequest.index(ML_MODEL_GROUP_INDEX).id(modelGroupID).setRefreshPolicy(WriteRequest.RefreshPolicy.IMMEDIATE);
             client.delete(deleteModelGroupRequest);