Fix validation of empty segment IDs in markUsed and markUnused APIs

[abhishekrb19]

Description:

Before this patch, isValid() treated empty segment IDs inconsistently. Consider the following scenarios with each parameter to markUsed and markUnused APIs and their outcomes:

1. Interval = null & segment IDs = null: Invalid
2. Interval = non-null & segment IDs = []: Invalid
3. Interval = non-null & segment IDs = null: Valid
4. Interval = null & segment IDs = []: Invalid

Note that in scenario 2, empty segment IDs are treated as the existence of the parameter. On the other hand, in scenario 4, empty segment IDs are treated as the absence of the parameter, which is confusing from an API user's perspective.

Fix:

With this patch, empty segment IDs are treated the same as null, indicating the absence of the parameter. So the outcome of scenario 2 will be Valid.

Added unit tests for the missing scenarios and updated the expectations of a couple of existing unit tests.

Release note

Fixed a bug in the markUsed and markUnused APIs where an empty set of segment IDs would be inconsistently treated as null or non-null in different scenarios.

This PR has:

• been self-reviewed.
• a release note entry in the PR description.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• been tested in a test Druid cluster.