Fixes #1854 CENTER, CHARGE and CLIENT data manager converted to kotlin. Includes minor fixes

[danishjamal104]

Fixes #1854

This PR includes dependency version update for mockito, 'org.mockito:mockito-core:1.10.19' >> testImplementation 'org.mockito:mockito-core:3.10.0'. Since older version of mockito doesn't support mocking the closed class and by default all Kotlin classes are closed, hence this upgrade has been done.

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[danishjamal104]

@iamsh4shank, @Grandolf49 please review and merge this. Thanks

[Aditya-gupta99]

We're closing this PR since it's already fixed