Merge branch 'master' into NH-2319

Author: fredericDelaporte

src/.gitignore

@@ -33,4 +33,5 @@ _ReSharper*/
 SharedAssemblyInfo.*
 hibernate.cfg.xml
 .vs/
-packages/
+packages/
+.idea/

src/NHibernate.Test/Async/Criteria/ProjectionsTest.cs

@@ -358,6 +358,29 @@ public async Task UseNotEqPropertyWithProjectionAsync()
 			}
 		}
 
+		[Test]
+		public async Task UseSumWithNullResultWithProjectionAsync()
+		{
+			using (ISession session = Sfi.OpenSession())
+			{
+				long sum = await (session.CreateCriteria(typeof(Reptile))
+					.SetProjection(Projections.Sum(Projections.Id()))
+					.UniqueResultAsync<long>());
+				Assert.AreEqual(0, sum);
+			}
+		}
 
+		[Test]
+		public async Task UseSubquerySumWithNullResultWithProjectionAsync()
+		{
+			using (ISession session = Sfi.OpenSession())
+			{
+				int sum = await (session.CreateCriteria(typeof(Enrolment))
+					.CreateCriteria("Student", "s")
+					.SetProjection(Projections.Sum(Projections.SqlFunction("length", NHibernateUtil.Int32, Projections.Property("s.Name"))))
+					.UniqueResultAsync<int>());
+				Assert.AreEqual(0, sum);
+			}
+		}
 	}
 }

src/NHibernate.Test/Criteria/ProjectionsTest.cs

@@ -347,6 +347,29 @@ public void UseNotEqPropertyWithProjection()
 			}
 		}
 
+		[Test]
+		public void UseSumWithNullResultWithProjection()
+		{
+			using (ISession session = Sfi.OpenSession())
+			{
+				long sum = session.CreateCriteria(typeof(Reptile))
+					.SetProjection(Projections.Sum(Projections.Id()))
+					.UniqueResult<long>();
+				Assert.AreEqual(0, sum);
+			}
+		}
 
+		[Test]
+		public void UseSubquerySumWithNullResultWithProjection()
+		{
+			using (ISession session = Sfi.OpenSession())
+			{
+				int sum = session.CreateCriteria(typeof(Enrolment))
+					.CreateCriteria("Student", "s")
+					.SetProjection(Projections.Sum(Projections.SqlFunction("length", NHibernateUtil.Int32, Projections.Property("s.Name"))))
+					.UniqueResult<int>();
+				Assert.AreEqual(0, sum);
+			}
+		}
 	}
 }

src/NHibernate/Async/Impl/CriteriaImpl.cs

@@ -110,19 +110,13 @@ public sealed partial class Subcriteria : ICriteria
 				return root.ListAsync<T>(cancellationToken);
 			}
 
-			public async Task<T> UniqueResultAsync<T>(CancellationToken cancellationToken = default(CancellationToken))
+			public Task<T> UniqueResultAsync<T>(CancellationToken cancellationToken = default(CancellationToken))
 			{
-				cancellationToken.ThrowIfCancellationRequested();
-				object result = await (UniqueResultAsync(cancellationToken)).ConfigureAwait(false);
-				if (result == null && typeof (T).IsValueType)
-				{
-					throw new InvalidCastException(
-						"UniqueResult<T>() cannot cast null result to value type. Call UniqueResult<T?>() instead");
-				}
-				else
+				if (cancellationToken.IsCancellationRequested)
 				{
-					return (T) result;
+					return Task.FromCanceled<T>(cancellationToken);
 				}
+				return root.UniqueResultAsync<T>(cancellationToken);
 			}
 
 			public Task<object> UniqueResultAsync(CancellationToken cancellationToken = default(CancellationToken))

src/NHibernate/Impl/CriteriaImpl.cs

@@ -808,16 +808,7 @@ public IList<T> List<T>()
 
 			public T UniqueResult<T>()
 			{
-				object result = UniqueResult();
-				if (result == null && typeof (T).IsValueType)
-				{
-					throw new InvalidCastException(
-						"UniqueResult<T>() cannot cast null result to value type. Call UniqueResult<T?>() instead");
-				}
-				else
-				{
-					return (T) result;
-				}
+				return root.UniqueResult<T>();
 			}
 
 			public void ClearOrders()