Add nil check for claimRef to avoid segmentation violation error

[HarishH-DELL]

Description

• Added a nil check to skip processing pvs without ClaimRef. This will prevent karavi-metrics-powermax from crashing when there are unbound pv s in clusters
• Enhanced unit tests to cover the same

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
dell/csm#1019

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have inspected the Grafana dashboards to verify the data is displayed properly
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have maintained backward compatibility

How Has This Been Tested?

Tested the scenario using unit tests and it looks good

[csmbot]

Can one of the admins verify this patch?

[gallacher]

run e2e test

[donatwork]

skip e2e test

[donatwork]

e2e pass