FE: Fix Default Consumer's Lag Value with nullish coalescing

[K-Diger]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

Reasons for setting up Git incorrectly
#686
created a new PR with the same content as the PR above.

close #675

The default value of Consumer Lag displayed when searching the Consumer List has been modified.

The existing displayed value is 'N/A', which is different from the response value of '0' that the server responds to.

We believe that 'N/A' may mean a state of disuse, so we write it as 0 to make it clear.

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

What changes did you make? (Give an overview)

Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• No need to
• Manually (please, describe, if necessary)
• Unit checks
• Integration checks
• Covered by existing automation

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• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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[Haarolean]

1. There's no need to spam with PRs, in favor of keeping the history. You can rebase or merge your PRs.
2. I still have no faintest clue what you are trying to achieve here
   As I mentioned in your previous PR (FE: Fix Default Consumer's Lag Value #686 (comment)), 0 and N/A are two distinct values.
   The current implementation looks fine, we interpret both values separately. With your changes, replacing a logical or with a bullish coalesce operator, you'd mutate the 0 value into being displayed as 0 rather than N/A.

Please cover your changes with unit tests, thanks.

[kapybro]

Further user feedback is requested. Please reply within 7 days or we might close the issue.

[K-Diger]

2. I still have no faintest clue what you are trying to achieve here

Before adding unit test code, I will first explain my position on your response.

The intention is to apply the results you tested in the console to the actual service.

When you test on the console, if 0 is assigned to the variable value,

When you run the existing code, you may have seen it displayed as 'N/A'.

However, in the code I modified, it be displayed as 0.

This is my intention with this example.

This is because 'N/A' has a different meaning from '0'.

To summarize again:
If the server responds with a Consumer Lag value of 0, it must be displayed as 0.

I only want to mark as N/A situations where Consumer Lag cannot be delivered due to an actual problem within the server, such as a Null on the server, or a problem within the Kafka ecosystem.

I think '0' and 'N/A' should be interpreted differently.

[kapybro]

Thanks for the additional feedback! We'll get back to your issue soon.