apache/druid · error · IllegalStateException

Cannot return long for Null Value

Error message

Cannot return long for Null Value

What it means

NullableNumericBufferAggregator keeps a null-marker byte in the ByteBuffer in front of each long value. getLong() throws IllegalStateException when that marker is IS_NULL_BYTE because a primitive long cannot represent null (0L would be ambiguous with a real zero).

Source

Thrown at processing/src/main/java/org/apache/druid/query/aggregation/NullableNumericBufferAggregator.java:102

      return null;
    }
    return delegate.get(buf, position + Byte.BYTES);
  }

  @Override
  public float getFloat(ByteBuffer buf, int position)
  {
    if (buf.get(position) == TypeStrategies.IS_NULL_BYTE) {
      throw new IllegalStateException("Cannot return float for Null Value");
    }
    return delegate.getFloat(buf, position + Byte.BYTES);
  }

  @Override
  public long getLong(ByteBuffer buf, int position)
  {
    if (buf.get(position) == TypeStrategies.IS_NULL_BYTE) {
      throw new IllegalStateException("Cannot return long for Null Value");
    }
    return delegate.getLong(buf, position + Byte.BYTES);
  }

  @Override
  public double getDouble(ByteBuffer buf, int position)
  {
    if (buf.get(position) == TypeStrategies.IS_NULL_BYTE) {
      throw new IllegalStateException("Cannot return double for Null Value");
    }
    return delegate.getDouble(buf, position + Byte.BYTES);
  }

  @Override
  public boolean isNull(ByteBuffer buf, int position)
  {
    return buf.get(position) == TypeStrategies.IS_NULL_BYTE || delegate.isNull(buf, position + Byte.BYTES);
  }

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Check agg.isNull(buf, position) before calling getLong()
2. Verify delegate reads use position + Byte.BYTES so the value, not the flag byte, is decoded
3. Ensure init()/putNull() in TypeStrategies initialize the marker byte for new group positions
4. If a group unexpectedly has no non-null values, that is a legitimate null result — handle it upstream instead of forcing a read

Example fix

// before
long v = agg.getLong(buf, position);
// after
Long v = agg.isNull(buf, position) ? null : agg.getLong(buf, position);

if (agg.isNull(buf, position)) {
  return null;
}

try {
  return agg.getLong(buf, position);
} catch (IllegalStateException e) {
  if (e.getMessage().contains("Cannot return long for Null Value")) {
    return null;
  }
  throw e;
}

When it happens

Trigger: Calling getLong(buf, position) when the byte at `position` is TypeStrategies.IS_NULL_BYTE — the group never aggregated a non-null long value.

Common situations: Long aggregations in group-by queries where some groups have only null inputs; buffer layout bugs where reads don't skip the flag byte (position vs position + Byte.BYTES); custom aggregators integrated without the nullable wrapper's buffer protocol.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Cannot return float for Null Value
• Cannot return double for Null Value
• Cannot return float for Null Value
• Cannot return long for Null Value
• Cannot return double for Null Value

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/43e652eddb87258f. Report an issue: GitHub.