NH-3096 - Linq add support for Nullable`1.GetValueOrDefault() without arguments

Author: hazzik

src/NHibernate.Test/Linq/ByMethod/GetValueOrDefaultTests.cs

@@ -25,5 +25,15 @@ public void GetValueOrDefaultInWhere()
 
 			Assert.AreEqual(830, orders.Count);
 		}
+
+		[Test]
+		public void GetValueOrDefaultWithSingleArgumentInWhere()
+		{
+			var orders = db.Orders
+						   .Where(x => x.Freight.GetValueOrDefault() > 0)
+						   .ToList();
+
+			Assert.AreEqual(830, orders.Count);
+		}
 	}
 }

src/NHibernate/Linq/Functions/GetValueOrDefaultGenerator.cs

@@ -28,7 +28,17 @@ public IEnumerable<MethodInfo> SupportedMethods
 
 		public HqlTreeNode BuildHql(MethodInfo method, Expression targetObject, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
 		{
-			return treeBuilder.Coalesce(visitor.Visit(targetObject).AsExpression(), visitor.Visit(arguments[0]).AsExpression());
+			return treeBuilder.Coalesce(visitor.Visit(targetObject).AsExpression(), GetRhs(method, arguments, treeBuilder, visitor));
+		}
+
+		private static HqlExpression GetRhs(MethodInfo method, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
+		{
+			if (arguments.Count > 0)
+				return visitor.Visit(arguments[0]).AsExpression();
+
+			var returnType = method.ReturnType;
+			var instance = returnType.IsValueType ? Activator.CreateInstance(returnType) : null;
+			return treeBuilder.Constant(instance);
 		}
 	}
 }