Fix Issue #4502 - Confusing exception when trying to map types with …

src/AutoMapper/ConstructorMap.cs

@@ -70,6 +70,8 @@ public class ConstructorParameterMap : MemberMap
     public ConstructorParameterMap(TypeMap typeMap, ParameterInfo parameter, MemberInfo[] sourceMembers) : base(typeMap)
     {
         Parameter = parameter;
+        var parameterType = parameter.ParameterType;
+        DestinationType = parameterType.IsByRef ? parameterType.GetElementType() : parameterType;
         if (sourceMembers.Length > 0)
         {
             MapByConvention(sourceMembers);
@@ -80,7 +82,7 @@ public ConstructorParameterMap(TypeMap typeMap, ParameterInfo parameter, MemberI
         }
     }
     public ParameterInfo Parameter { get; }
-    public override Type DestinationType => Parameter.ParameterType;
+    public override Type DestinationType { get; protected set; }
     public override IncludedMember IncludedMember { get; protected set; }
     public override MemberInfo[] SourceMembers { get; set; }
     public override string DestinationName => Parameter.Name;

src/UnitTests/Bug/ByrefConstructorParameter.cs

@@ -0,0 +1,41 @@
+namespace AutoMapper.UnitTests.Bug;
+
+public class ByrefConstructorParameter : AutoMapperSpecBase
+{
+    private Destination _destination;
+
+    class Source
+    {
+        public TimeSpan X { get; set; }
+    }
+
+    class Destination
+    {
+        public Destination(in TimeSpan x)
+        {
+            Y = x;
+        }
+
+        public TimeSpan Y { get; }
+    }
+
+    protected override MapperConfiguration CreateConfiguration() => new(cfg =>
+    {
+        cfg.CreateMap<Source, Destination>();
+    });
+
+    protected override void Because_of()
+    {
+        var source = new Source
+        {
+            X = TimeSpan.FromSeconds(17)
+        };
+        _destination = Mapper.Map<Destination>(source);
+    }
+
+    [Fact]
+    public void should_just_work()
+    {
+        _destination.Y.ShouldBe(TimeSpan.FromSeconds(17));
+    }
+}