Fix bug related to empty package manager name in npm_and_yarn package manager

[kbukum1]

What are you trying to accomplish?

This PR fixes a bug in the npm_and_yarn/package_manager.rb file where an empty or undefined package manager name resulted in a NoMethodError (undefined method 'to_sym' for an instance of Hash). This error, as reported in Sentry Issue DELTAFORCE-11XD, occurred when package_manager_by_name was called with an invalid package manager name.

The update ensures that the method handles cases of empty or invalid package manager names gracefully, preventing to_sym from being called on unintended data types.

Anything you want to highlight for special attention from reviewers?

To resolve this issue, the code now checks the validity of the package manager name before calling to_sym. Reviewers should focus on the additional validation logic to confirm that it aligns with expected behavior for handling empty or missing package manager names.

How will you know you've accomplished your goal?

• Reproduction: The bug has been reproduced, and the fix prevents the error when an empty package manager name is used.
• Feature Validation: Tests have been added for cases where the package manager name is empty or invalid to ensure consistent behavior.

Checklist

• Complete test suite executed, ensuring all tests and linters pass.
• Additional tests added to cover scenarios with empty or invalid package manager names.
• Commit messages are clear and descriptive.
• Provided a detailed description, including the problem, solution, and relevant implementation details.
• Ensured the code is well-documented and easy to understand.