HDDS-10581. NPE in SummarySubCommand & DiskUsageSubCommand.

[ArafatKhan2198]

What changes were proposed in this pull request?

• This issue arose from direct calls to methods like .asInt() and .asText() on potentially null JsonNode objects returned by .get(String) when the expected keys were missing in the JSON response.

Cannot invoke "com.fasterxml.jackson.databind.JsonNode.asInt()" because the return value of
"com.fasterxml.jackson.databind.JsonNode.get(String)" is null

• To resolve this, we employed the .path(String) method followed by .asInt(defaultValue) or .asText(defaultValue) to safely access and convert JSON fields. The .path(String) method ensures a null-safe way to access JSON fields, returning a "missing node" instead of null for absent keys, thereby preventing NPEs. Furthermore, by specifying default values for .asInt(defaultValue) and .asText(defaultValue), we ensured that our code could handle missing or unexpected data gracefully, defaulting to a pre-defined value instead of crashing or behaving unpredictably.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-10581

How was this patch tested?

• Ran TestNSSummaryAdmin without a problem.
• And also the Fork CI ran successfully :-
  https://github.com/ArafatKhan2198/ozone/actions/runs/8408238070

[ArafatKhan2198]

@adoroszlai @devabhishekpal @devmadhuu Could you please take a look.

[adoroszlai]

Thanks @ArafatKhan2198 for the patch.