apache/iceberg · error · UnsupportedOperationException

Can't retrieve values from an empty struct

Error message

Can't retrieve values from an empty struct

What it means

EmptyStructLike is a StructLike representing a struct with zero fields (used for unpartitioned rows). This library throws UnsupportedOperationException from get() because there are no positions to read from; any positional access is by definition a caller bug.

Source

Thrown at api/src/main/java/org/apache/iceberg/EmptyStructLike.java:40

class EmptyStructLike implements StructLike, Serializable {

  private static final EmptyStructLike INSTANCE = new EmptyStructLike();

  private EmptyStructLike() {}

  static EmptyStructLike get() {
    return INSTANCE;
  }

  @Override
  public int size() {
    return 0;
  }

  @Override
  public <T> T get(int pos, Class<T> javaClass) {
    throw new UnsupportedOperationException("Can't retrieve values from an empty struct");
  }

  @Override
  public <T> void set(int pos, T value) {
    throw new UnsupportedOperationException("Can't modify an empty struct");
  }

  @Override
  public boolean equals(Object other) {
    if (this == other) {
      return true;
    }

    return other != null && getClass() == other.getClass();
  }

  @Override
  public int hashCode() {

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Check the partition type/spec field count before accessing positions; skip position access when the struct has 0 fields
2. Use the shared EMPTY instance only as a placeholder, never iterate its positions
3. If representing an actually-partitioned row, ensure the correct StructLike implementation (e.g. InternalRecordWrapper/Partitioning.partitionType based) is used instead of EmptyStructLike

Example fix

// before
Object value = partition.get(0, Object.class);
// after
if (spec.partitionType().fields().isEmpty()) {
  return; // unpartitioned: no partition values to read
}
Object value = partition.get(0, Object.class);

if (spec.partitionType().fields().isEmpty()) { /* skip positional access */ }

boolean isReadable(StructLike s, int pos) {
  return !(s instanceof EmptyStructLike) && pos >= 0;
}

try {
  value = structLike.get(pos, javaClass);
} catch (UnsupportedOperationException e) {
  value = null; // empty struct: no partition values
}

When it happens

Trigger: Calling get(pos, javaClass) on the EmptyStructLike instance, typically obtained via partition-type.toStructLike(...) or internal code accessing the partition struct of an unpartitioned table with pos >= 0.

Common situations: Custom scan/delete code that assumes a non-empty partition struct; iterating partition positions of a table created with PartitionSpec.unpartitioned(); generic StructLike projection code reused across partitioned and unpartitioned tables.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Can't modify an empty struct
• %s doesn't implement cleanupLevel
• %s doesn't implement cleanExpiredMetadata
• Does not support schema getter
• %s does not implement deleteFile

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/e8a1ad5aec9898c0. Report an issue: GitHub.