version 0.12: multi search with .Type("product") failes with null reference exception

[ThomasSkyldahl]

ConcreteTypeConverter.GetConcreteTypeUsingSelector can return null for type if the as the typeDict can contain null values for the type and that case isn't handled.

I think it would make sense to check if the type is null otherwise return the baseType

Here is the the required code to reproduce the issue:

the search document class:

// indexed type
public class Product
{
  public string Code { get; set; }
}

public class MultiSearchThrowsWhenTypeIsSpecified
{       
 static void Main(string[] args)
        {
            var nest = new ElasticClient(new ConnectionSettings(new Uri("http://localhost:9200")));
            var indexName = "multisearch-with-type-name-error";
            var typeName = "product";
            nest.IndexMany(
                new[] {
                    new Product { Code = "1234" }, 
                    new Product { Code = "5678" }
                },
                indexName, typeName, new SimpleBulkParameters { Refresh = true });

            var searchName = "products";

            var result = nest.MultiSearch(descriptor => descriptor.Search<Product>(searchName,
                b => b.Index(indexName)
// I think the issue is that the type name is specified
                    .Type(typeName)));

            result.GetResponse<Product>(searchName);
        }
}

[Mpdreamz]

Sorry for taking so long to respond to this issue, I take pride in responding to issues ASAP but dropped the ball here.

Thanks for reporting @ThomasSkyldahl !