diff --git a/ExpressMapper NET40/MappingServiceBase.cs b/ExpressMapper NET40/MappingServiceBase.cs
index a469458..c09a190 100644
--- a/ExpressMapper NET40/MappingServiceBase.cs	
+++ b/ExpressMapper NET40/MappingServiceBase.cs	
@@ -121,40 +121,34 @@ public Expression GetMemberMappingExpression(Expression left, Expression right,
             var destType = destNullableType ?? left.Type;
             var sourceType = sourceNullableType ?? right.Type;
 
-            if (ComplexMapCondition(sourceType, destType))
+            var customMapExpression = GetCustomMapExpression(right.Type, left.Type);
+            if (customMapExpression != null)
             {
-                var customMapExpression = GetCustomMapExpression(right.Type, left.Type);
-                if (customMapExpression != null)
-                {
-                    var srcExp = Expression.Variable(right.Type,
-                        string.Format("{0}Src", Guid.NewGuid().ToString("N")));
-                    var assignSrcExp = Expression.Assign(srcExp, right);
+                var srcExp = Expression.Variable(right.Type,
+                    string.Format("{0}Src", Guid.NewGuid().ToString("N")));
+                var assignSrcExp = Expression.Assign(srcExp, right);
 
-                    var destExp = Expression.Variable(left.Type,
-                        string.Format("{0}Dst", Guid.NewGuid().ToString("N")));
-                    var assignDestExp = Expression.Assign(destExp, left);
+                var destExp = Expression.Variable(left.Type,
+                    string.Format("{0}Dst", Guid.NewGuid().ToString("N")));
+                var assignDestExp = Expression.Assign(destExp, left);
 
-                    // try precise substitute visitor
-                    var substituteParameterVisitor =
-                        new PreciseSubstituteParameterVisitor(
-                            new KeyValuePair<ParameterExpression, ParameterExpression>(
-                                Expression.Variable(right.Type, "srcTyped"), srcExp),
-                            new KeyValuePair<ParameterExpression, ParameterExpression>(
-                                Expression.Variable(left.Type, "dstTyped"), destExp));
+                // try precise substitute visitor
+                var substituteParameterVisitor =
+                    new PreciseSubstituteParameterVisitor(
+                        new KeyValuePair<ParameterExpression, ParameterExpression>(
+                            Expression.Variable(right.Type, "srcTyped"), srcExp),
+                        new KeyValuePair<ParameterExpression, ParameterExpression>(
+                            Expression.Variable(left.Type, "dstTyped"), destExp));
 
-                    var blockExpression = substituteParameterVisitor.Visit(customMapExpression) as BlockExpression;
+                var blockExpression = substituteParameterVisitor.Visit(customMapExpression) as BlockExpression;
 
-                    var assignResultExp = Expression.Assign(left, destExp);
-                    var resultBlockExp = Expression.Block(new[] { srcExp, destExp }, assignSrcExp, assignDestExp, blockExpression, assignResultExp);
+                var assignResultExp = Expression.Assign(left, destExp);
 
-                    var checkNullExp =
-                         Expression.IfThenElse(Expression.Equal(right, Expression.Default(right.Type)),
-                            Expression.Assign(left, Expression.Default(left.Type)), resultBlockExp);
-
-                    var releaseExp = Expression.Block(new ParameterExpression[] { }, (right.Type.GetInfo().IsPrimitive || right.Type.GetInfo().IsValueType ? resultBlockExp : (Expression)checkNullExp));
+                return Expression.Block(new[] { srcExp, destExp }, assignSrcExp, assignDestExp, blockExpression, assignResultExp);
+            }
 
-                    return releaseExp;
-                }
+            if (ComplexMapCondition(sourceType, destType))
+            {
 
                 var returnTypeDifferenceVisitor = new ReturnTypeDifferenceVisitor(right);
                 returnTypeDifferenceVisitor.Visit(right);
@@ -196,7 +190,9 @@ public Expression GetMemberMappingExpression(Expression left, Expression right,
                 destNullableType,
                 sourceNullableType);
 
-            var conditionalExpression = nullCheckNestedMemberVisitor.CheckNullExpression != null ? Expression.Condition(nullCheckNestedMemberVisitor.CheckNullExpression, Expression.Assign(left, Expression.Default(left.Type)), binaryExpression) : (Expression)binaryExpression;
+            var conditionalExpression = nullCheckNestedMemberVisitor.CheckNullExpression != null ?
+                Expression.Condition(nullCheckNestedMemberVisitor.CheckNullExpression,
+                Expression.Assign(left, Expression.Default(left.Type)), binaryExpression) : binaryExpression;
 
             return conditionalExpression;
         }
@@ -446,7 +442,8 @@ internal static Expression ConvertCollection(Type destPropType,
             else
             {
                 ctor = destPropType.GetInfo().GetConstructors(BindingFlags.Public | BindingFlags.Instance).FirstOrDefault(
-                    ci => {
+                    ci =>
+                    {
                         var param = ci.GetParameters();
                         return param.Length == 1 && param[0].ParameterType.GetInfo().IsAssignableFrom(destList);
                     });
diff --git a/ExpressMapper.Tests NET40/BasicTests.cs b/ExpressMapper.Tests NET40/BasicTests.cs
index 4931d8f..bca558d 100644
--- a/ExpressMapper.Tests NET40/BasicTests.cs	
+++ b/ExpressMapper.Tests NET40/BasicTests.cs	
@@ -53,6 +53,16 @@ public void ParallelPrecompileCollectionTest()
             Parallel.Invoke(actions.ToArray());
         }
 
+        [Test]
+        public void RegisterCustomStringToStringTest()
+        {
+            Mapper.Register<TestDefaultDecimalToStringViewModel, TestDefaultDecimalToStringViewModel>();
+            Mapper.RegisterCustom<string, string>(src => src ?? "");
+            var tst = new TestDefaultDecimalToStringViewModel();
+            var result = Mapper.Map<TestDefaultDecimalToStringViewModel, TestDefaultDecimalToStringViewModel>(tst);
+            Assert.AreEqual(result.TestString, "");
+        }
+
         [Test]
         public void DefaultPrimitiveTypePropertyToStringTest()
         {
@@ -74,9 +84,9 @@ public void MemberMappingsHasHigherPriorityThanCaseSensetiveTest()
                 .Member(t => t.Enabled, s => s.enabled == "Y");
             Mapper.Compile();
 
-           var source = new Source { enabled = "N" };
-           var result = Mapper.Map<Source, TargetViewModel>(source);
-           Assert.AreEqual(result.Enabled, false);
+            var source = new Source { enabled = "N" };
+            var result = Mapper.Map<Source, TargetViewModel>(source);
+            Assert.AreEqual(result.Enabled, false);
         }
 
         [Test]
@@ -293,7 +303,7 @@ public void HiddenInheritedMemberMap()
             Assert.AreEqual(result, srcDst.Value);
         }
 
-        private void MapBaseMember<T, TN>(IMemberConfiguration<T,TN> mapConfig) 
+        private void MapBaseMember<T, TN>(IMemberConfiguration<T, TN> mapConfig)
             where T : Gift
             where TN : GiftViewModel
         {
@@ -948,7 +958,7 @@ public void ExistingSrcCollGreater()
                 Assert.AreEqual(result.Collection.ElementAt(i), testResult.Item3.Collection.ElementAt(i));
             }
         }
-        
+
         [Test]
         public void ExistingDestDestCollGreater()
         {
@@ -1201,7 +1211,7 @@ public void MemberCaseSensitivityGlobalMapTest()
             };
 
             var typoCaseViewModel = Mapper.Map<TypoCase, TypoCaseViewModel>(typoCase);
-            
+
             Assert.AreEqual(typoCaseViewModel.Id, Guid.Empty);
             Assert.AreEqual(typoCaseViewModel.Name, null);
             Assert.AreEqual(typoCase.TestId, typoCaseViewModel.TestId);