Enums 将可为null的枚举映射到null时自动映射引发NullReferenceException

我似乎不明白为什么AutoMapper会对此映射抛出异常：

public class MyDestinationType
{
    public MyCustomEnum? PropName { get; set; }
}

public enum MyCustomEnum
{
    Val1,
    Val2
}

Mapper.CreateMap<MySourceType, MyDestinationType>()
    .ForMember(d => d.PropName, o => o.ResolveUsing(s => 
    {
        if (s.Val1) return MyCustomEnum.Val1;
        else if (s.Val2) return MyCustomEnum.Val2;
        return null;
    }))
;

引发的异常是一个AutoMapperMappingException，它封装了另外两个AutoMapperMappingException。第四个也是最后一个InnerException是NullReferenceException。堆栈跟踪如下所示：

[NullReferenceException: Object reference not set to an instance of an object.]
   AutoMapper.Mappers.EnumMapper.Map(ResolutionContext context, IMappingEngineRunner mapper) +198
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +447

[AutoMapperMappingException: Trying to map System.Object to System.Nullable`1[[MyProject.MyCustomEnum, MyProject, Version=2.0.4784.16259, Culture=neutral, PublicKeyToken=null]].
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Destination property: PropName
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +519
   AutoMapper.Mappers.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap) +592

[AutoMapperMappingException: Trying to map System.Object to System.Nullable`1[[MyProject.MyCustomEnum, MyProject, Version=2.0.4784.16259, Culture=neutral, PublicKeyToken=null]].
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Destination property: PropName
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.Mappers.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap) +689
   AutoMapper.Mappers.PropertyMapMappingStrategy.Map(ResolutionContext context, IMappingEngineRunner mapper) +275
   AutoMapper.Mappers.TypeMapMapper.Map(ResolutionContext context, IMappingEngineRunner mapper) +273
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +447

[AutoMapperMappingException: Trying to map MyProject.MySourceType to MyProject.MyDestinationType.
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +519
   AutoMapper.MappingEngine.Map(Object source, Type sourceType, Type destinationType, Action`1 opts) +192
   AutoMapper.MappingEngine.Map(Object source, Type sourceType, Type destinationType) +196
   AutoMapper.MappingEngine.Map(Object source) +169
   AutoMapper.Mapper.Map(Object source) +107
   [Here is where my code calls Mapper.Map<MyDestinationType>(source)]

[NullReferenceException:对象引用未设置为对象的实例。]
AutoMapper.Mappers.EnumMapper.Map（ResolutionContext上下文，IMappingEngineRunner映射器）+198
AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map（ResolutionContext上下文）+447
[AutoMapperMappingException:尝试将System.Object映射到System.Nullable`1[[MyProject.MyCustomEnum，MyProject，Version=2.0.4784.16259，Culture=neutral，PublicKeyToken=null]]。
使用MyProject.MySourceType到MyProject.MyDestinationType的映射配置
目标属性：PropName
引发了类型为“AutoMapper.AutoMappingException”的异常。]
AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map（ResolutionContext上下文）+519
AutoMapper.Mappers.PropertyMappingStrategy.MapPropertyValue（ResolutionContext上下文、IMappingEngineRunner映射器、Object mappedObject、PropertyMap PropertyMap）+592
[AutoMapperMappingException:尝试将System.Object映射到System.Nullable`1[[MyProject.MyCustomEnum，MyProject，Version=2.0.4784.16259，Culture=neutral，PublicKeyToken=null]]。
使用MyProject.MySourceType到MyProject.MyDestinationType的映射配置
目标属性：PropName
引发了类型为“AutoMapper.AutoMappingException”的异常。]
AutoMapper.Mappers.PropertyMappingStrategy.MapPropertyValue（ResolutionContext上下文、IMappingEngineRunner映射器、Object mappedObject、PropertyMap PropertyMap）+689
AutoMapper.Mappers.PropertyMappingStrategy.Map（ResolutionContext上下文，IMappingEngineRunner mapper）+275
AutoMapper.Mappers.typemapper.Map（ResolutionContext上下文，IMappingEngineRunner映射器）+273
AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map（ResolutionContext上下文）+447
[AutoMapperMappingException:尝试将MyProject.MySourceType映射到MyProject.MyDestinationType。
使用MyProject.MySourceType到MyProject.MyDestinationType的映射配置
引发了类型为“AutoMapper.AutoMappingException”的异常。]
AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map（ResolutionContext上下文）+519
AutoMapper.MappingEngine.Map（对象源，类型sourceType，类型destinationType，操作'1 opts）+192
AutoMapper.MappingEngine.Map（对象源，类型sourceType，类型destinationType）+196
AutoMapper.MappingEngine.Map（对象源）+169
AutoMapper.Mapper.Map（对象源）+107
[这里是我的代码调用Mapper.Map（源代码）的地方]

同样，只有当解析将具有

PropName==null

时才会发生异常（例如，如果

s.Val1

和

s.Val2

都为false）。当映射解析为具有某些非空值的枚举时，不会发生异常

---

这是AutoMapper中的另一个bug吗？

您找到解决方案了吗？我遇到了同样的问题！？

[NullReferenceException: Object reference not set to an instance of an object.]
   AutoMapper.Mappers.EnumMapper.Map(ResolutionContext context, IMappingEngineRunner mapper) +198
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +447

[AutoMapperMappingException: Trying to map System.Object to System.Nullable`1[[MyProject.MyCustomEnum, MyProject, Version=2.0.4784.16259, Culture=neutral, PublicKeyToken=null]].
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Destination property: PropName
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +519
   AutoMapper.Mappers.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap) +592

[AutoMapperMappingException: Trying to map System.Object to System.Nullable`1[[MyProject.MyCustomEnum, MyProject, Version=2.0.4784.16259, Culture=neutral, PublicKeyToken=null]].
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Destination property: PropName
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.Mappers.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap) +689
   AutoMapper.Mappers.PropertyMapMappingStrategy.Map(ResolutionContext context, IMappingEngineRunner mapper) +275
   AutoMapper.Mappers.TypeMapMapper.Map(ResolutionContext context, IMappingEngineRunner mapper) +273
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +447

[AutoMapperMappingException: Trying to map MyProject.MySourceType to MyProject.MyDestinationType.
Using mapping configuration for MyProject.MySourceType to MyProject.MyDestinationType
Exception of type 'AutoMapper.AutoMapperMappingException' was thrown.]
   AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context) +519
   AutoMapper.MappingEngine.Map(Object source, Type sourceType, Type destinationType, Action`1 opts) +192
   AutoMapper.MappingEngine.Map(Object source, Type sourceType, Type destinationType) +196
   AutoMapper.MappingEngine.Map(Object source) +169
   AutoMapper.Mapper.Map(Object source) +107
   [Here is where my code calls Mapper.Map<MyDestinationType>(source)]