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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"UnionMapWriter fails to write fixed size binary","articleBody":"A UnionMapWriter will null out the entire map struct entry instead of setting the value to null:\n```\n                childWriter.value().fixedSizeBinary().writeNull();\n```\n\nActually hits `NullableStructWriter#writeNull` whereas UnionMapWriter should override `writeNull` and do a switch on the mode (though I'm not certain if null keys are valid).\n\n\nEDIT:\nActually, the issue is that `fixedSizeBinary` needs to be overriden! Very frustrating, but this call is not overridden and is instead invoking `UnionListWriter#fixedSizeBinary()`:\n\n```java\n  @Override\n  public FixedSizeBinaryWriter fixedSizeBinary() {\n    return this;\n  }\n```\n\nThe real impl needs to override like so:\n```java\n  @Override\n  public FixedSizeBinaryWriter fixedSizeBinary() {\n    switch (mode) {\n      case KEY:\n        return entryWriter.fixedSizeBinary(MapVector.KEY_NAME);\n      case VALUE:\n        return entryWriter.fixedSizeBinary(MapVector.VALUE_NAME);\n      default:\n        return this;\n    }\n  }\n```","author":{"url":"https://github.com/nbauernfeind","@type":"Person","name":"nbauernfeind"},"datePublished":"2025-02-04T18:24:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/586/arrow-java/issues/586"}