NH-3950 fix.

Author: fredericDelaporte

src/NHibernate/Impl/FutureValue.cs

@@ -1,47 +1,44 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace NHibernate.Impl
 {
-    internal class FutureValue<T> : IFutureValue<T>, IDelayedValue
-    {
-        public delegate IEnumerable<T> GetResult();
-
-        private readonly GetResult getResult;
-
-        public FutureValue(GetResult result)
-        {
-            getResult = result;
-        }
-
-        public T Value
-        {
-            get
-            {
-                var result = getResult();
+	internal class FutureValue<T> : IFutureValue<T>, IDelayedValue
+	{
+		public delegate IEnumerable<T> GetResult();
+
+		private readonly GetResult getResult;
+
+		public FutureValue(GetResult result)
+		{
+			getResult = result;
+		}
+
+		public T Value
+		{
+			get
+			{
+				var result = getResult();
+				if (ExecuteOnEval != null)
+					// When not null, ExecuteOnEval is fetched with PostExecuteTransformer from IntermediateHqlTree
+					// through ExpressionToHqlTranslationResults, which requires a IQueryable as input and directly
+					// yields the scalar result when the query is scalar.
+					return (T)ExecuteOnEval.DynamicInvoke(result.AsQueryable());
+
 				var enumerator = result.GetEnumerator();
 
 				if (!enumerator.MoveNext())
-				{
-				    var defVal = default(T);
-                    if (ExecuteOnEval != null)
-                        defVal = (T)ExecuteOnEval.DynamicInvoke(defVal);
-				    return defVal;
-				}
-
-                var val = enumerator.Current;
-
-                if (ExecuteOnEval != null)
-                    val = (T)ExecuteOnEval.DynamicInvoke(val);
-				    
-                return val;
-            }
-        }
-
-        public Delegate ExecuteOnEval
-        {
-            get; set;
-        }
-    }
+					return default(T);
+
+				return enumerator.Current;
+			}
+		}
+
+		public Delegate ExecuteOnEval
+		{
+			get; set;
+		}
+	}
 }