ABFS: fix NPE in getCaseInsensitiveEnum when fs.azure.fns.account.service.type is configured

[neeraj-kulkarni]

Summary

• getConfiguredServiceTypeForFNSAccounts() passed null as the defaultValue to getCaseInsensitiveEnum()
• When fs.azure.fns.account.service.type IS configured, getCaseInsensitiveEnum calls defaultValue.getDeclaringClass() to resolve the enum type — NPE if defaultValue is null
• Fix: pass getFsConfiguredServiceType() as the default, which is never null and semantically correct (fall back to the FS-level service type)

Root cause

// Before: passes null — crashes when key is set
return getCaseInsensitiveEnum(FS_AZURE_FNS_ACCOUNT_SERVICE_TYPE, null);

// After: passes a safe non-null default
return getCaseInsensitiveEnum(FS_AZURE_FNS_ACCOUNT_SERVICE_TYPE, getFsConfiguredServiceType());

This bug was latent in the Hadoop 3.5.0 ABFS code — it only manifests when a caller sets fs.azure.fns.account.service.type in the configuration. Dremio's WASB→ABFS shim (Prototype.initConf()) sets this key to BLOB for flat-namespace accounts, which triggered the NPE.

Test plan

• Unit test: configure fs.azure.fns.account.service.type=BLOB and verify getConfiguredServiceTypeForFNSAccounts() returns BLOB without NPE
• Existing ABFS tests pass