Added UTs for null handling in CaseTransform function. (#11721) #21214

Job	Run time
Pinot Quickstart on JDK 11	20m 33s
Pinot Unit Test Set 1 (temurin-11)	1h 7m 53s
Pinot Quickstart on JDK 17	21m 42s
Pinot Compatibility Regression Testing against release-0.12.1 on compatibility-verifier/sample-test-suite	43m 3s
Pinot Quickstart on JDK 20	20m 43s
Pinot Unit Test Set 1 (temurin-17)	54m 39s
Pinot Integration Test Set 1 (temurin-11)	54m 3s
Pinot Compatibility Regression Testing against release-1.0.0 on compatibility-verifier/sample-test-suite	44m 36s
Pinot Unit Test Set 1 (temurin-20)	53m 27s
Pinot Integration Test Set 1 (temurin-17)	55m 33s
Pinot Compatibility Regression Testing against master on compatibility-verifier/sample-test-suite	2m 13s
Pinot Unit Test Set 2 (temurin-11)	50m 15s
Pinot Integration Test Set 1 (temurin-20)	50m 42s
Pinot Unit Test Set 2 (temurin-17)	40m 18s
Pinot Integration Test Set 2 (temurin-11)	47m 23s
Pinot Unit Test Set 2 (temurin-20)	45m 5s
Pinot Integration Test Set 2 (temurin-17)	45m 13s
Pinot Integration Test Set 2 (temurin-20)	41m 53s
Pinot Linter Test Set	1m 54s
	12h 41m 8s

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