[FEATURE] Improve test coverage for MLEngine Class

[dhrubo-os]

We need to improve test coverage in our repo.

This issue will target only to improve test coverage for MLEngine.java class

From this url we can see where test coverage is missing for this class: https://app.codecov.io/gh/opensearch-project/ml-commons/blob/2.x/ml-algorithms%2Fsrc%2Fmain%2Fjava%2Forg%2Fopensearch%2Fml%2Fengine%2FMLEngine.java

[MyrtleTurtle22]

Hi, I'd like to contribute to this but I'm not sure how to start. Could you help me get started?

[dhrubo-os]

@divitr Looks like you are working on this issue. I'm assigning it to you.

[dhrubo-os]

@divitr could you please comment on this issue? Otherwise I can't assign it to you.

[divitr]

Sure!