fix: map to target from null value should return null

Author: chaowlert

src/Mapster.Tests/Mapster.Tests.csproj

@@ -9,6 +9,7 @@
         <PublicSign Condition=" '$(OS)' != 'Windows_NT' ">true</PublicSign>
     </PropertyGroup>
     <ItemGroup>
+        <PackageReference Include="ExpressionDebugger" Version="2.0.0" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
         <PackageReference Include="MSTest.TestAdapter" Version="1.4.0" />
         <PackageReference Include="MSTest.TestFramework" Version="1.4.0" />

src/Mapster.Tests/WhenMappingArrays.cs

@@ -2,6 +2,7 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Shouldly;
 using System.Collections.Generic;
+using System.Linq.Expressions;
 
 namespace Mapster.Tests
 {
@@ -22,6 +23,16 @@ public void Single_Dimensional_Array_Is_Mapped()
             target.Ints.ShouldBe(source.Ints);
         }
 
+        [TestMethod]
+        public void MapToTarget_With_Null_Value()
+        {
+            var source = new FooArray { Ints = null };
+            var target = new BarArray { Ints = new int[] { 1, 2, 3, 4, 5 } };
+
+            TypeAdapter.Adapt(source, target);
+            target.Ints.ShouldBeNull();
+        }
+
         [TestMethod]
         public void Multi_Dimensional_Array_Is_Mapped()
         {

src/Mapster/Adapters/BaseAdapter.cs

@@ -185,7 +185,7 @@ protected Expression CreateBlockExpressionBody(Expression source, Expression des
                     var compareNull = Expression.Equal(source, Expression.Constant(null, source.Type));
                     set = Expression.IfThenElse(
                         compareNull,
-                        Expression.Assign(result, destination ?? arg.DestinationType.CreateDefault()),
+                        Expression.Assign(result, arg.DestinationType.CreateDefault()),
                         set);
                 }
             }

src/Mapster/Mapster.csproj

@@ -16,9 +16,9 @@
         <PackageLicenseUrl>https://github.com/MapsterMapper/Mapster/blob/master/LICENSE</PackageLicenseUrl>
         <NetStandardImplicitPackageVersion Condition=" '$(TargetFramework)' == 'netstandard1.3' ">1.6.1</NetStandardImplicitPackageVersion>
         <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
-        <Version>3.3.0</Version>
+        <Version>3.3.1</Version>
         <RootNamespace>Mapster</RootNamespace>
-        <AssemblyVersion>3.3.0.0</AssemblyVersion>
+        <AssemblyVersion>3.3.1.0</AssemblyVersion>
     </PropertyGroup>
     <ItemGroup Condition="'$(TargetFramework)' == 'net40'">
         <Reference Include="Microsoft.CSharp" />