code refactor not to occur nullpointer exception

[dhrubo-os]

Description

[Without this change following error can happen:

java.lang.NullPointerException: Cannot invoke "java.lang.Boolean.booleanValue()" because "doesVersionCreateModelGroup" is null
	at org.opensearch.ml.model.MLModelManager.deleteOrUpdateModelGroup(MLModelManager.java:960) ~[?:?]
	at org.opensearch.ml.model.MLModelManager.deleteModel(MLModelManager.java:953) ~[?:?]
	at org.opensearch.ml.model.MLModelManager.lambda$registerModel$34(MLModelManager.java:858) [opensearch-ml-multi-tenancy-2.15.0-SNAPSHOT.jar:multi-tenancy-2.15.0-SNAPSHOT]
	at org.opensearch.core.action.ActionListener$1.onFailure(ActionListener.java:90) [opensearch-core-2.15.0.jar:2.15.0]
	at org.opensearch.ml.engine.ModelHelper.downloadAndSplit(ModelHelper.java:297) ~[?:?]
	at org.opensearch.ml.model.MLModelManager.registerModel(MLModelManager.java:774) ~[?:?]
	at org.opensearch.ml.model.MLModelManager.lambda$registerModelFromUrl$27(MLModelManager.java:749) ~[?:?]
	at org.opensearch.core.action.ActionListener$1.onResponse(ActionListener.java:82) [opensearch-core-2.15.0.jar:2.15.0]
	at org.opensearch.action.support.ThreadedActionListener$1.doRun(ThreadedActionListener.java:78) [opensearch-2.15.0.jar:2.15.0]
	at org.opensearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:941) [opensearch-2.15.0.jar:2.15.0]
	at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52) [opensearch-2.15.0.jar:2.15.0]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642) [?:?]
	at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]
	```
]

### Related Issues
Resolves #[Issue number to be closed when this PR is merged]
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### Check List
- [ ] New functionality includes testing.
- [ ] New functionality has been documented.
- [ ] API changes companion pull request [created](https://github.com/opensearch-project/opensearch-api-specification/blob/main/DEVELOPER_GUIDE.md).
- [ ] Commits are signed per the DCO using `--signoff`.
- [ ] Public documentation issue/PR [created](https://github.com/opensearch-project/documentation-website/issues/new/choose).

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