Fix empty collection not initialized

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentArrayHolder.java

@@ -129,6 +129,13 @@ public class PersistentArrayHolder extends AbstractPersistentCollection {
 		return result;
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert array == null;
+		array = Array.newInstance( persister.getElementClass(), 0 );
+		endRead();
+	}
+
 	@Override
 	public void injectLoadedState(PluralAttributeMapping attributeMapping, List loadingState) {
 		assert isInitializing();

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentBag.java

@@ -260,6 +260,13 @@ public class PersistentBag extends AbstractPersistentCollection implements List
 		return getOrphans( sn, bag, entityName, getSession() );
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert bag == null;
+		bag = (List) persister.getCollectionType().instantiate( 0 );
+		endRead();
+	}
+
 	@Override
 	public Object disassemble(CollectionPersister persister) {
 		final int length = bag.size();
@@ -294,7 +301,6 @@ public class PersistentBag extends AbstractPersistentCollection implements List
 		return !persister.isOneToMany();
 	}
 
-
 	// For a one-to-many, a <bag> is not really a bag;
 	// it is *really* a set, since it can't contain the
 	// same element twice. It could be considered a bug

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentIdentifierBag.java

@@ -372,6 +372,14 @@ public class PersistentIdentifierBag extends AbstractPersistentCollection implem
 		return getOrphans( sn.values(), values, entityName, getSession() );
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert identifiers == null;
+		identifiers = new HashMap<>();
+		values = new ArrayList<>();
+		endRead();
+	}
+
 	@Override
 	public void preInsert(CollectionPersister persister) throws HibernateException {
 		final Iterator itr = values.iterator();

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentList.java

@@ -98,6 +98,13 @@ public class PersistentList extends AbstractPersistentCollection implements List
 		return getOrphans( sn, list, entityName, getSession() );
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert list == null;
+		list = (List) persister.getCollectionType().instantiate( 0 );
+		endRead();
+	}
+
 	@Override
 	public boolean equalsSnapshot(CollectionPersister persister) throws HibernateException {
 		final Type elementType = persister.getElementType();

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentMap.java

@@ -109,6 +109,13 @@ public class PersistentMap extends AbstractPersistentCollection implements Map {
 		return getOrphans( sn.values(), map.values(), entityName, getSession() );
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert map == null;
+		map = (Map) persister.getCollectionType().instantiate( 0 );
+		endRead();
+	}
+
 	@Override
 	public boolean equalsSnapshot(CollectionPersister persister) throws HibernateException {
 		final Type elementType = persister.getElementType();

hibernate-core/src/main/java/org/hibernate/collection/internal/PersistentSet.java

@@ -113,6 +113,13 @@ public class PersistentSet extends AbstractPersistentCollection implements java.
 		return getOrphans( sn.keySet(), set, entityName, getSession() );
 	}
 
+	@Override
+	public void initializeEmptyCollection(CollectionPersister persister) {
+		assert set == null;
+		set = (Set) persister.getCollectionType().instantiate( 0 );
+		endRead();
+	}
+
 	@Override
 	public boolean equalsSnapshot(CollectionPersister persister) throws HibernateException {
 		final Type elementType = persister.getElementType();

hibernate-core/src/main/java/org/hibernate/collection/spi/PersistentCollection.java

@@ -447,4 +447,6 @@ public interface PersistentCollection {
 	 * @return The orphans
 	 */
 	Collection getOrphans(Serializable snapshot, String entityName);
+
+	void initializeEmptyCollection(CollectionPersister persister);
 }

hibernate-core/src/main/java/org/hibernate/event/internal/DefaultInitializeCollectionEventListener.java

@@ -72,6 +72,7 @@ public class DefaultInitializeCollectionEventListener implements InitializeColle
 					LOG.trace( "Collection not cached" );
 				}
 				ceLoadedPersister.initialize( ce.getLoadedKey(), source );
+				handlePotentiallyEmptyCollection( collection, source, ce, ceLoadedPersister );
 				if ( LOG.isTraceEnabled() ) {
 					LOG.trace( "Collection initialized" );
 				}
@@ -86,6 +87,21 @@ public class DefaultInitializeCollectionEventListener implements InitializeColle
 		}
 	}
 
+	private void handlePotentiallyEmptyCollection(
+			PersistentCollection collection,
+			SessionImplementor source,
+			CollectionEntry ce, CollectionPersister ceLoadedPersister) {
+		if ( !collection.wasInitialized() ) {
+			collection.initializeEmptyCollection( ceLoadedPersister );
+			org.hibernate.sql.results.internal.Helper.finalizeCollectionLoading(
+					source.getPersistenceContext(),
+					ceLoadedPersister,
+					collection,
+					ce.getLoadedKey()
+			);
+		}
+	}
+
 	/**
 	 * Try to initialize a collection from the cache
 	 *

hibernate-core/src/main/java/org/hibernate/sql/results/internal/Helper.java

@@ -10,7 +10,12 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
 
+import org.hibernate.collection.spi.PersistentCollection;
+import org.hibernate.engine.spi.BatchFetchQueue;
+import org.hibernate.engine.spi.CollectionEntry;
+import org.hibernate.engine.spi.PersistenceContext;
 import org.hibernate.engine.spi.SessionFactoryImplementor;
+import org.hibernate.persister.collection.CollectionPersister;
 import org.hibernate.sql.exec.spi.Callback;
 import org.hibernate.sql.results.ResultsLogger;
 import org.hibernate.sql.results.graph.DomainResultAssembler;
@@ -58,4 +63,31 @@ public class Helper {
 		}
 	}
 
+	public static void finalizeCollectionLoading(
+			PersistenceContext persistenceContext,
+			CollectionPersister collectionDescriptor,
+			PersistentCollection collectionInstance,
+			Object key) {
+		CollectionEntry collectionEntry = persistenceContext.getCollectionEntry( collectionInstance );
+		if ( collectionEntry == null ) {
+			collectionEntry = persistenceContext.addInitializedCollection(
+					collectionDescriptor,
+					collectionInstance,
+					key
+			);
+		}
+		else {
+			collectionEntry.postInitialize( collectionInstance );
+		}
+
+		if ( collectionDescriptor.getCollectionType().hasHolder() ) {
+			persistenceContext.addCollectionHolder( collectionInstance );
+		}
+
+		final BatchFetchQueue batchFetchQueue = persistenceContext.getBatchFetchQueue();
+		batchFetchQueue.removeBatchLoadableCollection( collectionEntry );
+
+		// todo (6.0) : there is other logic still needing to be implemented here.  caching, etc
+		// 		see org.hibernate.engine.loading.internal.CollectionLoadContext#endLoadingCollection in 5.x
+	}
 }

hibernate-core/src/main/java/org/hibernate/sql/results/internal/LoadingCollectionEntryImpl.java

@@ -11,10 +11,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
 
-import org.hibernate.collection.internal.PersistentArrayHolder;
 import org.hibernate.collection.spi.PersistentCollection;
-import org.hibernate.engine.spi.BatchFetchQueue;
-import org.hibernate.engine.spi.CollectionEntry;
 import org.hibernate.engine.spi.PersistenceContext;
 import org.hibernate.engine.spi.SharedSessionContractImplementor;
 import org.hibernate.persister.collection.CollectionPersister;
@@ -90,27 +87,7 @@ public class LoadingCollectionEntryImpl implements LoadingCollectionEntry {
 		final PersistenceContext persistenceContext = session.getPersistenceContext();
 		final CollectionPersister collectionDescriptor = getCollectionDescriptor();
 
-		CollectionEntry collectionEntry = persistenceContext.getCollectionEntry( collectionInstance );
+		Helper.finalizeCollectionLoading( persistenceContext, collectionDescriptor, collectionInstance, getKey() );
-		if ( collectionEntry == null ) {
-			collectionEntry = persistenceContext.addInitializedCollection(
-					collectionDescriptor,
-					getCollectionInstance(),
-					getKey()
-			);
-		}
-		else {
-			collectionEntry.postInitialize( collectionInstance );
-		}
-
-		if ( collectionDescriptor.getCollectionType().hasHolder() ) {
-			persistenceContext.addCollectionHolder( collectionInstance );
-		}
-
-		final BatchFetchQueue batchFetchQueue = persistenceContext.getBatchFetchQueue();
-		batchFetchQueue.removeBatchLoadableCollection( collectionEntry );
-
-		// todo (6.0) : there is other logic still needing to be implemented here.  caching, etc
-		// 		see org.hibernate.engine.loading.internal.CollectionLoadContext#endLoadingCollection in 5.x
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/sql/results/internal/StandardRowReader.java

@@ -13,7 +13,6 @@ import org.hibernate.query.named.RowReaderMemento;
 import org.hibernate.sql.exec.spi.Callback;
 import org.hibernate.sql.results.graph.collection.CollectionInitializer;
 import org.hibernate.sql.results.graph.DomainResultAssembler;
-import org.hibernate.sql.results.graph.entity.EntityInitializer;
 import org.hibernate.sql.results.graph.Initializer;
 import org.hibernate.sql.results.jdbc.spi.JdbcValuesSourceProcessingOptions;
 import org.hibernate.sql.results.jdbc.spi.JdbcValuesSourceProcessingState;
@@ -52,14 +51,6 @@ public class StandardRowReader<T> implements RowReader<T> {
 		this.callback = callback;
 
 		this.resultRow = new Object[assemblerCount];
-
-		for ( int i = 0; i < initializers.size(); i++ ) {
-			final Initializer initializer = initializers.get( i );
-			if ( initializer instanceof EntityInitializer ) {
-				final EntityInitializer entityInitializer = (EntityInitializer) initializer;
-
-			}
-		}
 	}
 
 	@Override