Handle null name in CSVRecord accessors under ignoreHeaderCase

[rootvector2]

ignoreHeaderCase backs the header map with a TreeMap on String.CASE_INSENSITIVE_ORDER whose comparator rejects null keys, so a null name throws NullPointerException from CSVRecord.isMapped/isSet/get (and get(Enum) with a null enum) where the default LinkedHashMap path returns false or throws the documented IllegalArgumentException. guard the null name in isMapped (a null name is never a mapped header) and get (report the missing mapping) so the contract is the same regardless of ignoreHeaderCase; isSet is fixed transitively. found by passing a null name to the accessors under ignoreHeaderCase.

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[Copilot]

Pull request overview

This PR makes CSVRecord name-based accessors behave consistently when CSVFormat.Builder#setIgnoreHeaderCase(true) is enabled, preventing NullPointerException for null column names by treating null as “not mapped” and reporting a missing mapping via the documented IllegalArgumentException.

Changes:

• Guard null column names in CSVRecord.get(String) to avoid TreeMap/case-insensitive header map NullPointerException and throw IllegalArgumentException instead.
• Guard null column names in CSVRecord.isMapped(String) so it returns false consistently (and fixes isSet(String) via short-circuiting).
• Add a parameterized regression test covering both ignoreHeaderCase=false and true.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/main/java/org/apache/commons/csv/CSVRecord.java	Adds null guards in get(String) and isMapped(String) to align behavior across header-map implementations.
src/test/java/org/apache/commons/csv/CSVRecordTest.java	Adds a parameterized test ensuring null name accessors behave consistently regardless of ignoreHeaderCase.

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