From 773f64adac3925878c966990ef26d49290c9ba2a Mon Sep 17 00:00:00 2001
From: chaowlert <chaowlert@gmail.com>
Date: Sun, 22 Nov 2020 20:48:24 +0700
Subject: [PATCH] fix #281 null propagation

---
 src/Mapster.Tests/WhenFlattening.cs | 19 +++++++++++++++++++
 src/Mapster/Utils/ExpressionEx.cs   |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/src/Mapster.Tests/WhenFlattening.cs b/src/Mapster.Tests/WhenFlattening.cs
index a80d9858..da7f64d9 100644
--- a/src/Mapster.Tests/WhenFlattening.cs
+++ b/src/Mapster.Tests/WhenFlattening.cs
@@ -37,6 +37,11 @@ public class E
         public decimal BClass_Total { get; set; }
     }
 
+    public class F
+    {
+        public decimal? BClass_Total { get; set; }
+    }
+
     public class ModelObject
     {
         public DateTime BaseDate { get; set; }
@@ -106,6 +111,20 @@ public void PropertyTest_NameWithUnderscore()
             Assert.IsTrue(e.BClass_Total == 250);
         }
 
+        [TestMethod]
+        public void PropertyTest_NullPropagation()
+        {
+            var f = TypeAdapter.Adapt<C, F>(new C { BClass = new B { Total = 250 } });
+
+            Assert.IsNotNull(f);
+            Assert.IsTrue(f.BClass_Total == 250);
+
+            var f2 = TypeAdapter.Adapt<C, F>(new C { BClass = null });
+
+            Assert.IsNotNull(f2);
+            Assert.IsNull(f2.BClass_Total);
+        }
+
         [TestMethod]
         public void ShouldUseNestedObjectPropertyMembers()
         {
diff --git a/src/Mapster/Utils/ExpressionEx.cs b/src/Mapster/Utils/ExpressionEx.cs
index fd67f84f..06923eb9 100644
--- a/src/Mapster/Utils/ExpressionEx.cs
+++ b/src/Mapster/Utils/ExpressionEx.cs
@@ -317,6 +317,8 @@ public static Expression ApplyNullPropagation(this Expression getter)
                 if (expr.CanBeNull())
                 {
                     var compareNull = Expression.Equal(expr, Expression.Constant(null, expr.Type));
+                    if (!result.Type.CanBeNull())
+                        result = Expression.Convert(result, typeof(Nullable<>).MakeGenericType(result.Type));
                     result = Expression.Condition(compareNull, result.Type.CreateDefault(), result);
                 }