fix: guard nullable navigation in ProjectToType record ctor mapping (#898)

When a nullable navigation maps to a record DTO constructor parameter,
skip nested mapping when the source is null instead of evaluating
record ctor args against a null navigation. Also track NullChecks by
expression identity so nested projection parameters are not skipped
solely because they share a nullable type with a parent getter.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: wyf027

src/Mapster.Tests/WhenAddCtorNullablePropagation.cs

@@ -1,5 +1,5 @@
-using Mapster.Tests.Classes;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Shouldly;
 using System.Collections.Generic;
 using System.Linq;
 
@@ -15,14 +15,25 @@ public class WhenAddCtorNullablePropagation
         [TestMethod]
         public void NullablePropagationFromCtorWorking()
         {
-            var source = new List<OrderEntity898>();
+            var source = new List<OrderEntity898>
+            {
+                new() { Id = 1, Cod = new OrderCodEntity898 { Value = 42L } },
+                new() { Id = 2, Cod = null },
+            };
 
-            source.Add(new OrderEntity898() { Id = 1, Cod = new OrderCodEntity898 { Value = 42L } });
-            source.Add(new OrderEntity898() { Id = 2, Cod = null });
-
-            var str = new OrderEntity898() { Id = 1, Cod = new OrderCodEntity898 { Value = 42L } }.BuildAdapter().CreateProjectionExpression<OrderDto898>();
+            Should.NotThrow(() =>
+            {
+                source.AsQueryable().BuildAdapter().CreateProjectionExpression<OrderDto898>();
+            });
 
             var result = source.AsQueryable().ProjectToType<OrderDto898>().ToList();
+
+            result.Count.ShouldBe(2);
+            result[0].Id.ShouldBe(1);
+            result[0].Cod.ShouldNotBeNull();
+            result[0].Cod!.Value.ShouldBe(42L);
+            result[1].Id.ShouldBe(2);
+            result[1].Cod.ShouldBeNull();
         }
 
     }

src/Mapster/Adapters/BaseClassAdapter.cs

@@ -218,9 +218,9 @@ protected Expression CreateInstantiationExpression(Expression source, ClassMappi
             var members = classConverter.Members;
 
             var arguments = new List<Expression>();
+            arg.Context.NullChecks.UnionWith(members.Where(x => x.Getter != null).Select(x => (x.Getter, arg)));
             foreach (var member in members)
             {
-                arg.Context.NullChecks.UnionWith(members.Where(x=>x.Getter != null).Select(x=>(x.Getter,arg)));
                 var parameterInfo = (ParameterInfo)member.DestinationMember.Info!;
                 Expression defaultConst;
                 Expression getter;
@@ -253,12 +253,13 @@ protected Expression CreateInstantiationExpression(Expression source, ClassMappi
                 else
                 {
 
-                    if (member.Getter.CanBeNull() && member.DestinationMember.Type.IsAbstractOrNotPublicCtor()
-                        && member.Ignore.Condition == null)
+                    if (member.Getter.CanBeNull() && member.Ignore.Condition == null
+                        && (member.DestinationMember.Type.IsAbstractOrNotPublicCtor()
+                            || member.DestinationMember.Type.UnwrapNullable().IsRecordType()))
                     {
                         var compareNull = Expression.Equal(member.Getter, Expression.Constant(null, member.Getter.Type));
                         getter = Expression.Condition(ExpressionEx.Not(compareNull),
-                            CreateAdaptExpression(member.Getter, member.DestinationMember.Type, arg, member),
+                            CreateAdaptExpressionCore(member.Getter, member.DestinationMember.Type, arg, member),
                            defaultConst);
                     }
                     else

src/Mapster/Utils/ExpressionEx.cs

@@ -453,18 +453,18 @@ public static Expression ApplyNullPropagationFromCtor(this Expression getter, Ex
             Expression? condition = null;
             var current = getter;
             var checks = arg.Context.NullChecks
-                .Where(x=> !object.ReferenceEquals(x.arg,arg))
-                .Select(x=>x.param?.Type);
+                .Where(x => !object.ReferenceEquals(x.arg, arg))
+                .Select(x => x.param);
 
             while (current != null) 
             {
                 Expression? compareNull = null;
 
                 if (current.CanBeNull() && current is not ParameterExpression)
                     compareNull = Expression.NotEqual(current, Expression.Constant(null, current.Type));
-                else if (current.CanBeNull() && current is ParameterExpression
-                    && !checks.Contains(current.Type))
-                    compareNull = Expression.NotEqual(current, Expression.Constant(null, current.Type));
+                else if (current.CanBeNull() && current is ParameterExpression param
+                    && !checks.Contains(param))
+                    compareNull = Expression.NotEqual(param, Expression.Constant(null, param.Type));
 
                 if (compareNull != null)
                 {