Fix More then one save in transaction with one-to-one relations throw exception.

Author: dpodzyuban

Src/NHibernate.Envers.Tests/Integration/OneToOne/BiDirectional/BidirectionalSaveTest.cs

@@ -0,0 +1,50 @@
+using NHibernate.Cfg;
+using NHibernate.Envers.Configuration;
+using NUnit.Framework;
+using SharpTestsEx;
+
+namespace NHibernate.Envers.Tests.Integration.OneToOne.BiDirectional
+{
+	public class BidirectionalSaveTest : TestBase
+	{
+		private const int id = 18;
+
+		public BidirectionalSaveTest(AuditStrategyForTest strategyType) : base(strategyType)
+		{
+		}
+
+		protected override void AddToConfiguration(Cfg.Configuration configuration)
+		{
+			configuration.SetEnversProperty(ConfigurationKey.GlobalWithModifiedFlag, true);
+		} 
+		
+
+		protected override void Initialize()
+		{
+			var entity = new BiRefEdEntity { Id = id, Data = "1" };
+
+			using (var tx = Session.BeginTransaction())
+			{
+				Session.Save(entity);
+
+				entity.Data = "2";
+				Session.Update(entity);
+				tx.Commit();
+			}
+		}
+
+		
+		[Test]
+		public void VerifyRevisionCount()
+		{
+			AuditReader().GetRevisions(typeof(BiRefEdEntity), id)
+				.Should().Have.SameSequenceAs(1);
+		}
+		
+		[Test]
+		public void VerifyHistory()
+		{
+			AuditReader().Find<BiRefEdEntity>(id, 1).Data.Should().Be.EqualTo("2");
+		}
+	}
+}

Src/NHibernate.Envers/Synchronization/Work/AddWorkUnit.cs

@@ -77,11 +77,10 @@ private IDictionary<string, object> mergeModifiedFlags(IDictionary<string, objec
 			{
 				if (propertyData.UsingModifiedFlag)
 				{
-					var lhsValue = (bool)lhs[propertyData.ModifiedFlagPropertyName];
-					if (lhsValue)
+					if (lhs.TryGetValue(propertyData.ModifiedFlagPropertyName, out var lhsUntypedValue))
 					{
-						var rhsValue = (bool) rhs[propertyData.ModifiedFlagPropertyName];
-						if (!rhsValue)
+						var lhsValue = (bool)lhsUntypedValue;
+						if (lhsValue)
 						{
 							rhs[propertyData.ModifiedFlagPropertyName] = true;
 						}