IllegalArgumentException: BinaryIndexer allows only positive values

[bachlge]

Some of my data have negative (or zero) Key values.
When I add them to a GigaMap which has a BinaryIndexerLong, i'm getting an IllegalArgumentException:

java.lang.IllegalArgumentException: Only positive values are allowed: 0 in index com.gork.data.eclipsestore.model.AbstractEntityWithId.BinaryIndexerLong.Abstract
	at org.eclipse.store.gigamap.types.BinaryIndexer$Static.validate(BinaryIndexer.java:125) ~[gigamap-3.0.1.jar:na]

Question:
is there a technical reason for that restriction defined in validate(BinaryIndexer.java:125)?
or is there another recommended option for a numeric binary index that can handle negative key values? or IndexerLong?

Thank you in advance for your time and support.

this is my GigaMap and Entity defining the index:

abstract class Entities<ET extends AbstractEntityWithId<ET>> extends LockScope {

	public final GigaMap<ET> entities = GigaMap.<ET>Builder()
			.withBitmapIdentityIndex(ET.idIndex)
			.build();
	...
}


public abstract class AbstractEntityWithId<ET> extends AbstractEntity<ET> {

	/**
	 * Id-Index
	 */
	public static final BinaryIndexerLong<AbstractEntityWithId<?>> idIndex = new BinaryIndexerLong.Abstract<>() {
		@Override
		public Long getLong(AbstractEntityWithId<?> entity) {
			return entity.id;
		}
	};

	protected Long id;

	public Long getId() {
		return id;
	}
	...
}