diff --git a/src/NHibernate.Test/NHSpecificTest/NH901/Fixture.cs b/src/NHibernate.Test/NHSpecificTest/NH901/Fixture.cs
index bc430d8d8a4..35e39ce1c87 100644
--- a/src/NHibernate.Test/NHSpecificTest/NH901/Fixture.cs
+++ b/src/NHibernate.Test/NHSpecificTest/NH901/Fixture.cs
@@ -1,19 +1,13 @@
+using System.Collections;
+using NHibernate.Cfg;
+using NHibernate.Mapping.ByCode;
+using NHibernate.Type;
 using NUnit.Framework;
 
-using System;
-using System.Collections.Generic;
-using System.Text;
-
 namespace NHibernate.Test.NHSpecificTest.NH901
 {
-	[TestFixture]
-	public class Fixture : BugTestCase
+	public abstract class FixtureBase : TestCase
 	{
-		public override string BugNumber
-		{
-			get { return "NH901"; }
-		}
-
 		private new ISession OpenSession(IInterceptor interceptor)
 		{
 			lastOpenedSession = sessions.OpenSession(interceptor);
@@ -99,12 +93,56 @@ public void ReplaceValueTypeComponentWithSameValueDoesNotMakeItDirty()
 		}
 	}
 
+	[TestFixture]
+	public class Fixture : FixtureBase
+	{
+		protected override string MappingsAssembly
+		{
+			get { return "NHibernate.Test"; }
+		}
+
+		protected override IList Mappings
+		{
+			get { return new[] {"NHSpecificTest.NH901.Mappings.hbm.xml"}; }
+		}
+	}
+
+	[TestFixture]
+	public class FixtureByCode : FixtureBase
+	{
+		protected override IList Mappings
+		{
+			get { return new string[0]; }
+		}
+
+		protected override string MappingsAssembly
+		{
+			get { return null; }
+		}
+
+		protected override void AddMappings(Configuration configuration)
+		{
+			var mapper = new ModelMapper();
+			mapper.Class<Person>(rc =>
+			{
+				rc.Table("NH901_Person");
+				rc.Id(x => x.Name, m => m.Generator(Generators.Assigned));
+				rc.Component(x => x.Address, cm =>
+				{
+					cm.Property(x => x.City);
+					cm.Property(x => x.Street);
+				});
+			});
+			configuration.AddMapping(mapper.CompileMappingForAllExplicitlyAddedEntities());
+		}
+	}
+
 	public class InterceptorStub : EmptyInterceptor
 	{
 		public object entityToCheck;
 		public bool entityWasDeemedDirty = false;
 
-		public override bool OnFlushDirty(object entity, object id, object[] currentState, object[] previousState, string[] propertyNames, NHibernate.Type.IType[] types)
+		public override bool OnFlushDirty(object entity, object id, object[] currentState, object[] previousState, string[] propertyNames, IType[] types)
 		{
 			if (entity == entityToCheck) { entityWasDeemedDirty = true; }
 
diff --git a/src/NHibernate/Mapping/ByCode/Conformist/ComponentMapping.cs b/src/NHibernate/Mapping/ByCode/Conformist/ComponentMapping.cs
index 37f27aa0299..91791587b14 100644
--- a/src/NHibernate/Mapping/ByCode/Conformist/ComponentMapping.cs
+++ b/src/NHibernate/Mapping/ByCode/Conformist/ComponentMapping.cs
@@ -3,7 +3,7 @@
 
 namespace NHibernate.Mapping.ByCode.Conformist
 {
-	public class ComponentMapping<T> : ComponentCustomizer<T> where T : class
+	public class ComponentMapping<T> : ComponentCustomizer<T>
 	{
 		public ComponentMapping() : base(new ExplicitDeclarationsHolder(), new CustomizersHolder()) { }
 	}
diff --git a/src/NHibernate/Mapping/ByCode/IBagPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/IBagPropertiesMapper.cs
index 6cd38f10b83..dcd47449d39 100644
--- a/src/NHibernate/Mapping/ByCode/IBagPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IBagPropertiesMapper.cs
@@ -2,5 +2,6 @@ namespace NHibernate.Mapping.ByCode
 {
 	public interface IBagPropertiesMapper : ICollectionPropertiesMapper {}
 
-	public interface IBagPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement> where TEntity : class {}
+	public interface IBagPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
+	{}
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/IClassMapper.cs b/src/NHibernate/Mapping/ByCode/IClassMapper.cs
index 5e715cf1075..e16e41d2758 100644
--- a/src/NHibernate/Mapping/ByCode/IClassMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IClassMapper.cs
@@ -47,10 +47,10 @@ public interface IClassAttributesMapper<TEntity> : IEntityAttributesMapper, IEnt
 		void Id<TProperty>(Expression<Func<TEntity, TProperty>> idProperty, Action<IIdMapper> idMapper);
 		void Id(string notVisiblePropertyOrFieldName, Action<IIdMapper> idMapper);
 
-		void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty) where TComponent : class;
-		void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty, Action<IComponentAsIdMapper<TComponent>> idMapper) where TComponent : class;
-		void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName) where TComponent : class;
-		void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentAsIdMapper<TComponent>> idMapper) where TComponent : class;
+		void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty);
+		void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty, Action<IComponentAsIdMapper<TComponent>> idMapper);
+		void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName);
+		void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentAsIdMapper<TComponent>> idMapper);
 
 		void ComposedId(Action<IComposedIdMapper<TEntity>> idPropertiesMapping);
 
diff --git a/src/NHibernate/Mapping/ByCode/ICollectionPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/ICollectionPropertiesMapper.cs
index 442359a3dc2..2bf5c4d570b 100644
--- a/src/NHibernate/Mapping/ByCode/ICollectionPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/ICollectionPropertiesMapper.cs
@@ -31,7 +31,7 @@ public interface ICollectionPropertiesMapper : IEntityPropertyMapper, ICollectio
 		void Persister(System.Type persister);
 	}
 
-	public interface ICollectionPropertiesMapper<TEntity, TElement> : IEntityPropertyMapper, ICollectionSqlsMapper where TEntity : class
+	public interface ICollectionPropertiesMapper<TEntity, TElement> : IEntityPropertyMapper, ICollectionSqlsMapper
 	{
 		void Inverse(bool value);
 		void Mutable(bool value);
diff --git a/src/NHibernate/Mapping/ByCode/IComponentMapper.cs b/src/NHibernate/Mapping/ByCode/IComponentMapper.cs
index bd6d7113bd3..3ca8969afcd 100644
--- a/src/NHibernate/Mapping/ByCode/IComponentMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IComponentMapper.cs
@@ -28,5 +28,6 @@ public interface IComponentAttributesMapper<TComponent> : IEntityPropertyMapper
 		void Class<TConcrete>() where TConcrete : TComponent;
 	}
 
-	public interface IComponentMapper<TComponent> : IComponentAttributesMapper<TComponent>, IPropertyContainerMapper<TComponent> where TComponent : class {}
+	public interface IComponentMapper<TComponent> : IComponentAttributesMapper<TComponent>, IPropertyContainerMapper<TComponent>
+	{}
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/IDynamicComponentAttributesMapper.cs b/src/NHibernate/Mapping/ByCode/IDynamicComponentAttributesMapper.cs
index 016742ae55c..d580b5cc1e7 100644
--- a/src/NHibernate/Mapping/ByCode/IDynamicComponentAttributesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IDynamicComponentAttributesMapper.cs
@@ -16,6 +16,7 @@ public interface IDynamicComponentAttributesMapper<TComponent> : IEntityProperty
 		void Unique(bool unique);
 	}
 
-	public interface IDynamicComponentMapper<TComponent> : IDynamicComponentAttributesMapper<TComponent>, IPropertyContainerMapper<TComponent> where TComponent : class { }
+	public interface IDynamicComponentMapper<TComponent> : IDynamicComponentAttributesMapper<TComponent>, IPropertyContainerMapper<TComponent>
+	{ }
 
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/IIdBagPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/IIdBagPropertiesMapper.cs
index 94317db6430..79711f42312 100644
--- a/src/NHibernate/Mapping/ByCode/IIdBagPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IIdBagPropertiesMapper.cs
@@ -6,7 +6,7 @@ public interface IIdBagPropertiesMapper : ICollectionPropertiesMapper
 		void Id(Action<ICollectionIdMapper> idMapping);
 	}
 
-	public interface IIdBagPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement> where TEntity : class
+	public interface IIdBagPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
 	{
 		void Id(Action<ICollectionIdMapper> idMapping);		
 	}
diff --git a/src/NHibernate/Mapping/ByCode/IKeyMapper.cs b/src/NHibernate/Mapping/ByCode/IKeyMapper.cs
index fe4d10add5f..3afd6de5563 100644
--- a/src/NHibernate/Mapping/ByCode/IKeyMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IKeyMapper.cs
@@ -29,7 +29,7 @@ public interface IKeyMapper : IColumnsMapper
 		void ForeignKey(string foreignKeyName);
 	}
 
-	public interface IKeyMapper<TEntity> : IColumnsMapper where TEntity : class
+	public interface IKeyMapper<TEntity> : IColumnsMapper
 	{
 		void OnDelete(OnDeleteAction deleteAction);
 		void PropertyRef<TProperty>(Expression<Func<TEntity, TProperty>> propertyGetter);
diff --git a/src/NHibernate/Mapping/ByCode/IListPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/IListPropertiesMapper.cs
index 9d9c01c4ade..793ec934afe 100644
--- a/src/NHibernate/Mapping/ByCode/IListPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IListPropertiesMapper.cs
@@ -7,7 +7,7 @@ public interface IListPropertiesMapper : ICollectionPropertiesMapper
 		void Index(Action<IListIndexMapper> listIndexMapping);
 	}
 
-	public interface IListPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement> where TEntity : class
+	public interface IListPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
 	{
 		void Index(Action<IListIndexMapper> listIndexMapping);
 	}
diff --git a/src/NHibernate/Mapping/ByCode/IMapPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/IMapPropertiesMapper.cs
index c36e559c0ed..bc80464b0b1 100644
--- a/src/NHibernate/Mapping/ByCode/IMapPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IMapPropertiesMapper.cs
@@ -2,5 +2,6 @@ namespace NHibernate.Mapping.ByCode
 {
 	public interface IMapPropertiesMapper : ICollectionPropertiesMapper {}
 
-	public interface IMapPropertiesMapper<TEntity, TKey, TElement> : ICollectionPropertiesMapper<TEntity, TElement> where TEntity : class {}
+	public interface IMapPropertiesMapper<TEntity, TKey, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
+	{}
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/IPlainPropertyContainerMapper.cs b/src/NHibernate/Mapping/ByCode/IPlainPropertyContainerMapper.cs
index dec00aba56f..115eae3ef56 100644
--- a/src/NHibernate/Mapping/ByCode/IPlainPropertyContainerMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IPlainPropertyContainerMapper.cs
@@ -37,19 +37,13 @@ public interface IMinimalPlainPropertyContainerMapper<TContainer>
 
 	public interface IBasePlainPropertyContainerMapper<TContainer> : IMinimalPlainPropertyContainerMapper<TContainer>
 	{
-		void Component<TComponent>(Expression<Func<TContainer, TComponent>> property,
-															 Action<IComponentMapper<TComponent>> mapping) where TComponent : class;
-		void Component<TComponent>(Expression<Func<TContainer, TComponent>> property) where TComponent : class;
-		void Component<TComponent>(Expression<Func<TContainer, IDictionary>> property,
-								   TComponent dynamicComponentTemplate,
-								   Action<IDynamicComponentMapper<TComponent>> mapping) where TComponent : class;
-
-		void Component<TComponent>(string notVisiblePropertyOrFieldName,
-															 Action<IComponentMapper<TComponent>> mapping) where TComponent : class;
-		void Component<TComponent>(string notVisiblePropertyOrFieldName) where TComponent : class;
-		void Component<TComponent>(string notVisiblePropertyOrFieldName,
-															 TComponent dynamicComponentTemplate,
-															 Action<IDynamicComponentMapper<TComponent>> mapping) where TComponent : class;
+		void Component<TComponent>(Expression<Func<TContainer, TComponent>> property, Action<IComponentMapper<TComponent>> mapping);
+		void Component<TComponent>(Expression<Func<TContainer, TComponent>> property);
+		void Component<TComponent>(Expression<Func<TContainer, IDictionary>> property, TComponent dynamicComponentTemplate, Action<IDynamicComponentMapper<TComponent>> mapping);
+
+		void Component<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentMapper<TComponent>> mapping);
+		void Component<TComponent>(string notVisiblePropertyOrFieldName);
+		void Component<TComponent>(string notVisiblePropertyOrFieldName, TComponent dynamicComponentTemplate, Action<IDynamicComponentMapper<TComponent>> mapping);
 
 		void Any<TProperty>(Expression<Func<TContainer, TProperty>> property, System.Type idTypeOfMetaType, Action<IAnyMapper> mapping) where TProperty : class;
 		void Any<TProperty>(string notVisiblePropertyOrFieldName, System.Type idTypeOfMetaType, Action<IAnyMapper> mapping) where TProperty : class;
diff --git a/src/NHibernate/Mapping/ByCode/IPropertyContainerMapper.cs b/src/NHibernate/Mapping/ByCode/IPropertyContainerMapper.cs
index 843a24abb05..3375084659e 100644
--- a/src/NHibernate/Mapping/ByCode/IPropertyContainerMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/IPropertyContainerMapper.cs
@@ -26,7 +26,7 @@ void IdBag(MemberInfo property, Action<IIdBagPropertiesMapper> collectionMapping
 
 	public interface IPropertyContainerMapper : ICollectionPropertiesContainerMapper, IPlainPropertyContainerMapper {}
 
-	public interface ICollectionPropertiesContainerMapper<TEntity> where TEntity : class
+	public interface ICollectionPropertiesContainerMapper<TEntity>
 	{
 		void Set<TElement>(Expression<Func<TEntity, IEnumerable<TElement>>> property,
 		                   Action<ISetPropertiesMapper<TEntity, TElement>> collectionMapping,
@@ -92,5 +92,6 @@ void IdBag<TElement>(string notVisiblePropertyOrFieldName,
 											 Action<IIdBagPropertiesMapper<TEntity, TElement>> collectionMapping);
 	}
 
-	public interface IPropertyContainerMapper<TEntity> : ICollectionPropertiesContainerMapper<TEntity>, IPlainPropertyContainerMapper<TEntity> where TEntity : class {}
+	public interface IPropertyContainerMapper<TEntity> : ICollectionPropertiesContainerMapper<TEntity>, IPlainPropertyContainerMapper<TEntity>
+	{}
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/ISetPropertiesMapper.cs b/src/NHibernate/Mapping/ByCode/ISetPropertiesMapper.cs
index a906d7d34e3..0be79f70849 100644
--- a/src/NHibernate/Mapping/ByCode/ISetPropertiesMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/ISetPropertiesMapper.cs
@@ -2,5 +2,6 @@ namespace NHibernate.Mapping.ByCode
 {
 	public interface ISetPropertiesMapper : ICollectionPropertiesMapper {}
 
-	public interface ISetPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement> where TEntity : class {}
+	public interface ISetPropertiesMapper<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
+	{}
 }
\ No newline at end of file
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/BagPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/BagPropertiesCustomizer.cs
index dfb5fd825d7..a6ee995d8f2 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/BagPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/BagPropertiesCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class BagPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IBagPropertiesMapper<TEntity, TElement> where TEntity : class
+	public class BagPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IBagPropertiesMapper<TEntity, TElement>
 	{
 		public BagPropertiesCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, PropertyPath propertyPath, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, propertyPath, customizersHolder)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ClassCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ClassCustomizer.cs
index d2de6bdf921..1364bba265e 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ClassCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ClassCustomizer.cs
@@ -66,29 +66,29 @@ public void Id(string notVisiblePropertyOrFieldName, Action<IIdMapper> idMapper)
 			CustomizersHolder.AddCustomizer(typeof(TEntity), m => m.Id(member, idMapper));
 		}
 
-		public void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty) where TComponent : class
+		public void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty)
 		{
 			ComponentAsId(idProperty, x => { });
 		}
 
-		public void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty, Action<IComponentAsIdMapper<TComponent>> idMapper) where TComponent : class
+		public void ComponentAsId<TComponent>(Expression<Func<TEntity, TComponent>> idProperty, Action<IComponentAsIdMapper<TComponent>> idMapper)
 		{
 			var memberOf = TypeExtensions.DecodeMemberAccessExpressionOf(idProperty);
 			RegisterComponentAsIdMapping(idMapper, memberOf);
 		}
 
-		public void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName) where TComponent : class
+		public void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName)
 		{
 			ComponentAsId<TComponent>(notVisiblePropertyOrFieldName, x => { });
 		}
 
-		public void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentAsIdMapper<TComponent>> idMapper) where TComponent : class
+		public void ComponentAsId<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentAsIdMapper<TComponent>> idMapper)
 		{
 			var member = typeof(TEntity).GetPropertyOrFieldMatchingName(notVisiblePropertyOrFieldName);
 			RegisterComponentAsIdMapping(idMapper, member);
 		}
 
-		private void RegisterComponentAsIdMapping<TComponent>(Action<IComponentAsIdMapper<TComponent>> idMapper, params MemberInfo[] members) where TComponent : class
+		private void RegisterComponentAsIdMapping<TComponent>(Action<IComponentAsIdMapper<TComponent>> idMapper, params MemberInfo[] members)
 		{
 			foreach (var member in members)
 			{
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionKeyCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionKeyCustomizer.cs
index 51e409dcbe5..8d59cfadcda 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionKeyCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionKeyCustomizer.cs
@@ -5,7 +5,6 @@
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
 	public class CollectionKeyCustomizer<TEntity> : IKeyMapper<TEntity>
-		where TEntity : class
 	{
 		private readonly PropertyPath propertyPath;
 
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionPropertiesCustomizer.cs
index e79236f0f76..349969bc755 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/CollectionPropertiesCustomizer.cs
@@ -7,7 +7,6 @@
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
 	public class CollectionPropertiesCustomizer<TEntity, TElement> : ICollectionPropertiesMapper<TEntity, TElement>
-		where TEntity : class
 	{
 		private readonly IKeyMapper<TEntity> keyMapper;
 
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentAsIdCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentAsIdCustomizer.cs
index 7334a20f281..49f16ba51f4 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentAsIdCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentAsIdCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class ComponentAsIdCustomizer<TComponent> : PropertyContainerCustomizer<TComponent>, IComponentAsIdMapper<TComponent> where TComponent : class
+	public class ComponentAsIdCustomizer<TComponent> : PropertyContainerCustomizer<TComponent>, IComponentAsIdMapper<TComponent>
 	{
 		public ComponentAsIdCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, ICustomizersHolder customizersHolder, PropertyPath propertyPath)
 			: base(explicitDeclarationsHolder, customizersHolder, propertyPath)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentCustomizer.cs
index 80346ea5135..cb91ae7eef6 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ComponentCustomizer.cs
@@ -5,7 +5,6 @@
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
 	public class ComponentCustomizer<TComponent> : PropertyContainerCustomizer<TComponent>, IComponentMapper<TComponent>, IConformistHoldersProvider
-		where TComponent : class
 	{
 		public ComponentCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, customizersHolder, null)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/DynamicComponentCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/DynamicComponentCustomizer.cs
index c08d14ecfd2..d409c6d57ee 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/DynamicComponentCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/DynamicComponentCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class DynamicComponentCustomizer<TComponent> : PropertyContainerCustomizer<TComponent>, IDynamicComponentMapper<TComponent> where TComponent : class
+	public class DynamicComponentCustomizer<TComponent> : PropertyContainerCustomizer<TComponent>, IDynamicComponentMapper<TComponent>
 	{
 		public DynamicComponentCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, ICustomizersHolder customizersHolder, PropertyPath propertyPath)
 			: base(explicitDeclarationsHolder, customizersHolder, propertyPath)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/IdBagPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/IdBagPropertiesCustomizer.cs
index 171d6157e8e..878fed3904a 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/IdBagPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/IdBagPropertiesCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class IdBagPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IIdBagPropertiesMapper<TEntity, TElement> where TEntity : class
+	public class IdBagPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IIdBagPropertiesMapper<TEntity, TElement>
 	{
 		public IdBagPropertiesCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, PropertyPath propertyPath, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, propertyPath, customizersHolder)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ListPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ListPropertiesCustomizer.cs
index 04f2143f6fb..5901550aa6c 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ListPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/ListPropertiesCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class ListPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IListPropertiesMapper<TEntity, TElement> where TEntity : class
+	public class ListPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IListPropertiesMapper<TEntity, TElement>
 	{
 		public ListPropertiesCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, PropertyPath propertyPath, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, propertyPath, customizersHolder)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/MapPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/MapPropertiesCustomizer.cs
index 0195d196eaf..0114c941c96 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/MapPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/MapPropertiesCustomizer.cs
@@ -3,7 +3,6 @@
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
 	public class MapPropertiesCustomizer<TEntity, TKey, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, IMapPropertiesMapper<TEntity, TKey, TElement>
-		where TEntity : class
 	{
 		public MapPropertiesCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, PropertyPath propertyPath, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, propertyPath, customizersHolder)
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/PropertyContainerCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/PropertyContainerCustomizer.cs
index 4ea5ec54b80..b3119f6244a 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/PropertyContainerCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/PropertyContainerCustomizer.cs
@@ -6,7 +6,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class PropertyContainerCustomizer<TEntity> where TEntity : class
+	public class PropertyContainerCustomizer<TEntity>
 	{
 		private readonly IModelExplicitDeclarationsHolder explicitDeclarationsHolder;
 
@@ -69,26 +69,23 @@ protected void RegistePropertyMapping(Action<IPropertyMapper> mapping, params Me
 		}
 
 		public void Component<TComponent>(Expression<Func<TEntity, TComponent>> property, Action<IComponentMapper<TComponent>> mapping)
-			where TComponent : class
 		{
 			RegisterComponentMapping(property, mapping);
 		}
 
-		public void Component<TComponent>(Expression<Func<TEntity, TComponent>> property) where TComponent : class
+		public void Component<TComponent>(Expression<Func<TEntity, TComponent>> property)
 		{
 			RegisterComponentMapping(property, x => { });
 		}
 
 		protected virtual void RegisterComponentMapping<TComponent>(Expression<Func<TEntity, TComponent>> property, Action<IComponentMapper<TComponent>> mapping)
-			where TComponent : class
 		{
 			MemberInfo member = TypeExtensions.DecodeMemberAccessExpression(property);
 			MemberInfo memberOf = TypeExtensions.DecodeMemberAccessExpressionOf(property);
-			RegisterComponentMapping<TComponent>(mapping, member, memberOf);
+			RegisterComponentMapping(mapping, member, memberOf);
 		}
 
 		protected void RegisterComponentMapping<TComponent>(Action<IComponentMapper<TComponent>> mapping, params MemberInfo[] members)
-			where TComponent : class
 		{
 			foreach (var member in members)
 			{
@@ -96,22 +93,19 @@ protected void RegisterComponentMapping<TComponent>(Action<IComponentMapper<TCom
 			}
 		}
 
-		public void Component<TComponent>(Expression<Func<TEntity, IDictionary>> property,
-													 TComponent dynamicComponentTemplate,
-													 Action<IDynamicComponentMapper<TComponent>> mapping) where TComponent : class
+		public void Component<TComponent>(Expression<Func<TEntity, IDictionary>> property, TComponent dynamicComponentTemplate, Action<IDynamicComponentMapper<TComponent>> mapping)
 		{
 			RegisterDynamicComponentMapping(property, mapping);
 		}
 
-		protected virtual void RegisterDynamicComponentMapping<TComponent>(Expression<Func<TEntity, IDictionary>> property, Action<IDynamicComponentMapper<TComponent>> mapping) where TComponent : class
+		protected virtual void RegisterDynamicComponentMapping<TComponent>(Expression<Func<TEntity, IDictionary>> property, Action<IDynamicComponentMapper<TComponent>> mapping)
 		{
 			MemberInfo member = TypeExtensions.DecodeMemberAccessExpression(property);
 			MemberInfo memberOf = TypeExtensions.DecodeMemberAccessExpressionOf(property);
-			RegisterDynamicComponentMapping<TComponent>(mapping, member, memberOf);
+			RegisterDynamicComponentMapping(mapping, member, memberOf);
 		}
 
 		protected void RegisterDynamicComponentMapping<TComponent>(Action<IDynamicComponentMapper<TComponent>> mapping, params MemberInfo[] members)
-			where TComponent : class
 		{
 			foreach (var member in members)
 			{
@@ -463,7 +457,7 @@ public void ManyToOne<TProperty>(string notVisiblePropertyOrFieldName, Action<IM
 			RegisterManyToOneMapping<TProperty>(mapping, member, memberOf);
 		}
 
-		public void Component<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentMapper<TComponent>> mapping) where TComponent : class
+		public void Component<TComponent>(string notVisiblePropertyOrFieldName, Action<IComponentMapper<TComponent>> mapping)
 		{
 			MemberInfo member = GetPropertyOrFieldMatchingNameOrThrow(notVisiblePropertyOrFieldName);
 			var propertyOrFieldType = member.GetPropertyOrFieldType();
@@ -476,12 +470,12 @@ public void Component<TComponent>(string notVisiblePropertyOrFieldName, Action<I
 			RegisterComponentMapping<TComponent>(mapping, member, memberOf);
 		}
 
-		public void Component<TComponent>(string notVisiblePropertyOrFieldName) where TComponent : class
+		public void Component<TComponent>(string notVisiblePropertyOrFieldName)
 		{
 			Component<TComponent>(notVisiblePropertyOrFieldName, x => { });
 		}
 
-		public void Component<TComponent>(string notVisiblePropertyOrFieldName, TComponent dynamicComponentTemplate, Action<IDynamicComponentMapper<TComponent>> mapping) where TComponent : class
+		public void Component<TComponent>(string notVisiblePropertyOrFieldName, TComponent dynamicComponentTemplate, Action<IDynamicComponentMapper<TComponent>> mapping)
 		{
 			MemberInfo member = GetPropertyOrFieldMatchingNameOrThrow(notVisiblePropertyOrFieldName);
 			MemberInfo memberOf = member.GetMemberFromReflectedType(typeof(TEntity));
diff --git a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/SetPropertiesCustomizer.cs b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/SetPropertiesCustomizer.cs
index e6ff2b146c7..dd733697ebe 100644
--- a/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/SetPropertiesCustomizer.cs
+++ b/src/NHibernate/Mapping/ByCode/Impl/CustomizersImpl/SetPropertiesCustomizer.cs
@@ -2,7 +2,7 @@
 
 namespace NHibernate.Mapping.ByCode.Impl.CustomizersImpl
 {
-	public class SetPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, ISetPropertiesMapper<TEntity, TElement> where TEntity : class
+	public class SetPropertiesCustomizer<TEntity, TElement> : CollectionPropertiesCustomizer<TEntity, TElement>, ISetPropertiesMapper<TEntity, TElement>
 	{
 		public SetPropertiesCustomizer(IModelExplicitDeclarationsHolder explicitDeclarationsHolder, PropertyPath propertyPath, ICustomizersHolder customizersHolder)
 			: base(explicitDeclarationsHolder, propertyPath, customizersHolder)
diff --git a/src/NHibernate/Mapping/ByCode/ModelMapper.cs b/src/NHibernate/Mapping/ByCode/ModelMapper.cs
index 08360fc805d..b4624ec934d 100644
--- a/src/NHibernate/Mapping/ByCode/ModelMapper.cs
+++ b/src/NHibernate/Mapping/ByCode/ModelMapper.cs
@@ -526,7 +526,7 @@ public void UnionSubclass<TEntity>(Action<IUnionSubclassMapper<TEntity>> customi
 			customizeAction(customizer);
 		}
 
-		public void Component<TComponent>(Action<IComponentMapper<TComponent>> customizeAction) where TComponent : class
+		public void Component<TComponent>(Action<IComponentMapper<TComponent>> customizeAction)
 		{
 			var customizer = new ComponentCustomizer<TComponent>(explicitDeclarationsHolder, customizerHolder);
 			customizeAction(customizer);