From dce29b6461f6c0e2a046f6d013270f5a8a396282 Mon Sep 17 00:00:00 2001
From: wuyangfan <yangfan.wu@succaiss.com>
Date: Mon, 25 May 2026 14:03:13 +0800
Subject: [PATCH] fix: skip abstract base mapping when nested source is null
 (#928)

When a nullable abstract/base property is mapped with Include<> configured,
Mapster attempted to adapt through the abstract destination type even when
the source value was null, throwing "Cannot instantiate type" at runtime.

Short-circuit null sources before adapting to abstract or non-public-ctor
destination types in CreateAdaptExpression.

Co-authored-by: Cursor <cursoragent@cursor.com>
---
 .../WhenMappingNullableAbstractWithInclude.cs | 78 +++++++++++++++++++
 src/Mapster/Adapters/BaseAdapter.cs           |  7 ++
 2 files changed, 85 insertions(+)
 create mode 100644 src/Mapster.Tests/WhenMappingNullableAbstractWithInclude.cs

diff --git a/src/Mapster.Tests/WhenMappingNullableAbstractWithInclude.cs b/src/Mapster.Tests/WhenMappingNullableAbstractWithInclude.cs
new file mode 100644
index 00000000..8cbef55f
--- /dev/null
+++ b/src/Mapster.Tests/WhenMappingNullableAbstractWithInclude.cs
@@ -0,0 +1,78 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Shouldly;
+
+namespace Mapster.Tests
+{
+    [TestClass]
+    public class WhenMappingNullableAbstractWithInclude
+    {
+        [TestMethod]
+        public void Null_Abstract_Property_With_Include_Maps_To_Null()
+        {
+            var config = new TypeAdapterConfig();
+            config.Default.MapToConstructor(true);
+            config
+                .NewConfig<DtoBase, DomainBase>()
+                .Include<DtoDerived, DomainDerived>();
+
+            var dto = new DtoFoo { Field = null };
+
+            var domain = dto.Adapt<DomainFoo>(config);
+
+            domain.Field.ShouldBeNull();
+        }
+
+        [TestMethod]
+        public void Derived_Abstract_Property_With_Include_Maps_To_Derived_Domain()
+        {
+            var config = new TypeAdapterConfig();
+            config.Default.MapToConstructor(true);
+            config
+                .NewConfig<DtoBase, DomainBase>()
+                .Include<DtoDerived, DomainDerived>();
+
+            var dto = new DtoFoo
+            {
+                Field = new DtoDerived { Id = "id" },
+            };
+
+            var domain = dto.Adapt<DomainFoo>(config);
+
+            domain.Field.ShouldNotBeNull();
+            domain.Field.ShouldBeOfType<DomainDerived>();
+            ((DomainDerived)domain.Field).Id.ShouldBe("id");
+        }
+
+        #region test classes
+
+        public abstract class DtoBase
+        {
+        }
+
+        public class DtoDerived : DtoBase
+        {
+            public string Id { get; set; } = null!;
+        }
+
+        public class DtoFoo
+        {
+            public DtoBase? Field { get; set; }
+        }
+
+        public abstract class DomainBase
+        {
+        }
+
+        public class DomainDerived : DomainBase
+        {
+            public string Id { get; set; } = null!;
+        }
+
+        public class DomainFoo
+        {
+            public DomainBase? Field { get; set; }
+        }
+
+        #endregion
+    }
+}
diff --git a/src/Mapster/Adapters/BaseAdapter.cs b/src/Mapster/Adapters/BaseAdapter.cs
index b31a0dbe..fbe69b7f 100644
--- a/src/Mapster/Adapters/BaseAdapter.cs
+++ b/src/Mapster/Adapters/BaseAdapter.cs
@@ -520,6 +520,13 @@ internal Expression CreateAdaptExpression(Expression source, Type destinationTyp
             else
                 exp = CreateAdaptExpressionCore(_source, destinationType, arg, mapping, destination);
 
+            if (notUsingDestinationValue
+                && _source.CanBeNull()
+                && destinationType.IsAbstractOrNotPublicCtor())
+            {
+                exp = _source.NotNullReturn(exp);
+            }
+
             //transform(adapt(_source));
             if (notUsingDestinationValue)
             {