Fix generating coalesce for Boolean expressions

Fixes #1468

Author: hazzik

src/NHibernate.Test.VisualBasic/Issues/GH1468/Entity.vb

@@ -0,0 +1,7 @@
+Namespace Issues.GH1468
+    Public Class Entity
+        Public Overridable Property Id As Guid
+
+        Public Overridable Property Date1 As Date?
+    End Class
+End Namespace

src/NHibernate.Test.VisualBasic/Issues/GH1468/Fixture.vb

@@ -0,0 +1,81 @@
+Imports NUnit.Framework
+
+Namespace Issues.GH1468
+    <TestFixture>
+    Public Class Fixture
+        Inherits IssueTestCase
+
+        Protected Overrides Sub OnSetUp()
+
+            Using session As ISession = OpenSession()
+
+                Using transaction As ITransaction = session.BeginTransaction()
+
+                    Dim e1 = New Entity
+                    e1.Date1 = new Date(2017, 12, 3)
+                    session.Save(e1)
+
+                    Dim e2 = New Entity
+                    e2.Date1 = new Date(2017, 12, 1)
+                    session.Save(e2)
+
+                    Dim e3 = New Entity
+                    session.Save(e3)
+
+                    session.Flush()
+                    transaction.Commit()
+
+                End Using
+
+            End Using
+        End Sub
+
+        Protected Overrides Sub OnTearDown()
+
+            Using session As ISession = OpenSession()
+
+                Using transaction As ITransaction = session.BeginTransaction()
+
+                    session.Delete("from System.Object")
+
+                    session.Flush()
+                    transaction.Commit()
+
+                End Using
+
+            End Using
+        End Sub
+
+        <Test>
+        Public Sub ShouldBeAbleToCompareNullableDate()
+
+            Using session As ISession = OpenSession()
+                Using session.BeginTransaction()
+
+                    Dim d = New Date(2017, 12, 2)
+                    Dim result = (From e In session.Query (Of Entity)
+                            Where e.Date1 >= d
+                            Select e).ToList()
+
+                    Assert.AreEqual(1, result.Count)
+                End Using
+            End Using
+        End Sub
+
+        <Test>
+        Public Sub ShouldBeAbleToCompareNullableDateGetValueOrDefault()
+
+            Using session As ISession = OpenSession()
+                Using session.BeginTransaction()
+
+                    Dim d = New Date(2017, 12, 2)
+                    Dim result = (From e In session.Query (Of Entity)
+                            Where (e.Date1 >= d).GetValueOrDefault()
+                            Select e).ToList()
+
+                    Assert.AreEqual(1, result.Count)
+                End Using
+            End Using
+        End Sub
+    End Class
+End Namespace

src/NHibernate.Test.VisualBasic/Issues/GH1468/Issues.GH1468.Mappings.hbm.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernate.Test.VisualBasic" namespace="NHibernate.Test.VisualBasic.Issues.GH1468">
+
+	<class name="Entity">
+		<id name="Id">
+			<generator class="guid.comb"/>
+		</id>
+		<property name="Date1" />
+	</class>
+
+</hibernate-mapping>

src/NHibernate/Linq/Functions/GetValueOrDefaultGenerator.cs

@@ -28,13 +28,13 @@ 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(), GetRhs(method, arguments, treeBuilder, visitor));
+			return treeBuilder.Coalesce(visitor.Visit(targetObject).ToArithmeticExpression(), 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();
+				return visitor.Visit(arguments[0]).ToArithmeticExpression();
 
 			var returnType = method.ReturnType;
 			var instance = returnType.IsValueType ? Activator.CreateInstance(returnType) : null;

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionVisitor.cs

@@ -8,7 +8,6 @@
 using NHibernate.Param;
 using NHibernate.Util;
 using Remotion.Linq.Clauses.Expressions;
-using Remotion.Linq.Clauses.ResultOperators;
 
 namespace NHibernate.Linq.Visitors
 {
@@ -316,7 +315,7 @@ protected HqlTreeNode VisitBinaryExpression(BinaryExpression expression)
 					return _hqlTreeBuilder.GreaterThanOrEqual(lhs, rhs);
 
 				case ExpressionType.Coalesce:
-					return _hqlTreeBuilder.Coalesce(lhs, rhs);
+					return _hqlTreeBuilder.Coalesce(lhs.ToArithmeticExpression(), rhs.ToArithmeticExpression());
 			}
 
 			throw new InvalidOperationException();