Handle null in oldElements

Author: bahusoid

src/NHibernate/Async/Collection/AbstractPersistentCollection.cs

@@ -193,15 +193,18 @@ protected virtual async Task<ICollection> GetOrphansAsync(ICollection oldElement
 			}
 
 			List<object> res = new List<object>();
-			// oldElements may contain new elements in some cases
+			// oldElements may contain new elements (one case when session.Save is called on new object with list)
 			foreach (object old in oldElements)
 			{
-				var id = persister.GetIdentifier(old);
-				if (id != null)
+				if (old != null)
 				{
-					if (!currentObjects.Contains(id) && await (ForeignKeys.IsNotTransientSlowAsync(persister.EntityName, old, Session, cancellationToken)).ConfigureAwait(false))
+					var id = persister.GetIdentifier(old);
+					if (id != null)
 					{
-						res.Add(old);
+						if (!currentObjects.Contains(id) && await (ForeignKeys.IsNotTransientSlowAsync(persister.EntityName, old, Session, cancellationToken)).ConfigureAwait(false))
+						{
+							res.Add(old);
+						}
 					}
 				}
 			}

src/NHibernate/Collection/AbstractPersistentCollection.cs

@@ -735,15 +735,18 @@ protected virtual ICollection GetOrphans(ICollection oldElements, ICollection cu
 			}
 
 			List<object> res = new List<object>();
-			// oldElements may contain new elements in some cases
+			// oldElements may contain new elements (one case when session.Save is called on new object with list)
 			foreach (object old in oldElements)
 			{
-				var id = persister.GetIdentifier(old);
-				if (id != null)
+				if (old != null)
 				{
-					if (!currentObjects.Contains(id) && ForeignKeys.IsNotTransientSlow(persister.EntityName, old, Session))
+					var id = persister.GetIdentifier(old);
+					if (id != null)
 					{
-						res.Add(old);
+						if (!currentObjects.Contains(id) && ForeignKeys.IsNotTransientSlow(persister.EntityName, old, Session))
+						{
+							res.Add(old);
+						}
 					}
 				}
 			}