determine the types of arguments for generic method is incorrect

I use Dapper.Contrib to insert my Entity, my code like this

cn.Insert(instance);

when the type of entity instance is created by emit , the generic method in Dapper.Contrib.Extensions.SqlMapperExtensions

public static long Insert<T>(this IDbConnection connection, T entityToInsert, IDbTransaction transaction = null, int? commandTimeout = null) where T : class
{
            var isList = false;

            var type = typeof(T);

            if (type.IsArray)
            {
                isList = true;
                type = type.GetElementType();
            }
  // other codes
}

can't determine the types of entityToInsert correct, because var type = typeof(T); return typeof(object)

here is the sourcecode https://github.com/StackExchange/Dapper/blob/master/Dapper.Contrib/SqlMapperExtensions.cs#L332

Start in SqlMapperExtensions.cs around the Insert method at the referenced line and reproduce the case where an emitted entity is passed through cn.Insert(instance). Trace how the entity type is determined, then verify that inserts use the entity's actual type rather than object and add or run a regression test for the emitted entity case.