Use of the EnableEnumMappingValidation throws NullReferenceException

[trejjam]

Mapping configuration

new MapperConfiguration(c =>
{
  c.EnableEnumMappingValidation();
  c.CreateMap<object, object>();
})

Version: 3.0.0

Expected behavior

It validates mapping and does not throw exception

Actual behavior

System.NullReferenceException: Object reference not set to an instance of an object.
   at AutoMapper.Features.Features`1.GetEnumerator()
   at AutoMapper.Extensions.EnumMapping.EnumMapperConfigurationExpressionExtensions.<>c.<EnableEnumMappingValidation>b__0_0(ValidationContext context)
   at AutoMapper.Configuration.ConfigurationValidator.Validate(ValidationContext context)
   at AutoMapper.Configuration.ConfigurationValidator.DryRunTypeMap(IGlobalConfiguration config, HashSet`1 typeMapsChecked, TypePair types, TypeMap typeMap, MemberMap memberMap)
   at AutoMapper.Configuration.ConfigurationValidator.AssertConfigurationIsValid(IGlobalConfiguration config, IEnumerable`1 typeMaps)

Steps to reproduce

new MapperConfiguration(c =>
{
  c.EnableEnumMappingValidation();
  c.CreateMap<object, object>();
}).AssertConfigurationIsValid();

[lbargaoanu]

A PR is welcome.

[HenkKin]

I found the issue, tomorrow I hope to offer a pull request.

            mapperConfigurationExpression.Internal().Validator(context =>
            {
                if (context.TypeMap != null) // FIX:  && context.TypeMap.Features != null && context.TypeMap.Features.Count > 0)
                {
                    foreach (var feature in context.TypeMap.Features) <-- this one throws NullReferenceException if count is 0, would be nice to return an empty enumerator in AutoMapper
                    {
                        if (feature is IEnumMappingValidationRuntimeFeature validator)
                        {
                            validator.Validate(context.TypeMap.Types);
                        }
                    }
                }
            });

[lbargaoanu]

The fix is in this repo, replace the foreach with Get<TFeature>(). Enumeration is for internal use.

[trejjam]

I tried to use the context.TypeMap.Features.Get<IEnumMappingValidationRuntimeFeature>(). The issue is that Get search by GetType of searched items, which is the EnumMappingValidationRuntimeFeature<TSource, TDestination>. And in the Features.Get<IEnumMappingValidationRuntimeFeature>() context you do not have TSource, TDestination.

There are several ways how to solve it.
a) Create proxy class EnumMappingValidationRuntimeFeature which can be called without TSource, TDestination:

internal class EnumMappingValidationRuntimeFeature : IEnumMappingValidationRuntimeFeature
{
private readonly IEnumMappingValidationRuntimeFeature  _innerValidationRuntimeFeature;
public EnumMappingValidationRuntimeFeature(IEnumMappingValidationRuntimeFeature innerValidationRuntimeFeature)
{
  _innerValidationRuntimeFeature = innerValidationRuntimeFeature;
}

void IEnumMappingValidationRuntimeFeature.Validate(TypePair typePair) => _innerValidationRuntimeFeature.Validate(typePair);
}

b) Add GetAssignableTo<T> into the Features<TFeature>.
c) use reflection and call Get<EnumMappingValidationRuntimeFeature<TSource, TDestination>>()

Which one do you like?

[trejjam]

I created PR with the first option

[HenkKin]

Released!