[Forwardport] Correct return type of methods and typo correction.

[saurabh-parekh]

Original Pull Request

#15993

Description

Correct return type of methods and change return type.

Fixed Issues (if relevant)

N/A

Manual testing scenarios

N/A

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @saurabh-aureate. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
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[magento-engcom-team]

Hi @saurabh-aureate. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.