title: NullReferenceException when inserting with Dapper
body: <p>When I run the following code I get a NullReferenceException saying that an object reference not set to an instance of the object.  I've successfully inserted with dapper using less complex objects but the same format, so am not sure what I'm doing wrong.</p>
  
  <pre><code>public void Foo(IEnumerable&lt;FogbugzCase&gt; cases) 
  {
      // using a singleton for the SqlConnection
      using (SqlConnection conn = CreateConnection())
      {
          foreach (FogbugzCase fogbugzCase in cases)
          {
              conn.Execute("INSERT INTO fogbugz.Cases(CaseId, Title, ProjectId, CategoryId, Root, MilestoneId, Priority, Status, EstimatedHours, ElapsedHours, AssignedTo, ResolvedBy, IsResolved, IsOpen, Opened, Resolved, Uri, ResolveUri, OutlineUri, SpecUri, ParentId, Backlog) VALUES(@BugId, @Title, @ProjectId, @CategoryId, @RootId, @MilestoneId, @Priority, @StatusId, @EstimatedHours, @ElapsedHours, @PersonAssignedToId, @PersonResolvedById, @IsResolved, @IsOpen, @Opened, @Resolved, @Uri, @ResolveUri, @OutlineUri, @Spec, @ParentId, @Backlog);", new {BugId = fogbugzCase.BugId, Title = fogbugzCase.Title, ProjectId = fogbugzCase.Project.Id, CategoryId = fogbugzCase.Category.Id, RootId = fogbugzCase.Root, MilestoneId = fogbugzCase.Milestone.Id, Priority = fogbugzCase.Priority, StatusId = fogbugzCase.Status.Id, EstimatedHours = fogbugzCase.EstimatedHours, ElapsedHours = fogbugzCase.ElapsedHours, PersonAssignedToId = fogbugzCase.PersonAssignedTo.Id, PersonResolvedById = fogbugzCase.PersonResolvedBy.Id, IsResolved = fogbugzCase.IsResolved, IsOpen = fogbugzCase.IsOpen, Opened = fogbugzCase.Opened, Resolved = fogbugzCase.Resolved, Uri = fogbugzCase.Uri, OutlineUri = fogbugzCase.OutlineUri, Spec = fogbugzCase.Spec, ParentId = fogbugzCase.ParentId, Backlog = fogbugzCase.Backlog});
          }
      }
  }
  </code></pre>
  
  <p>I first tried doing the simpler way of just passing in <code>fogbugzCase</code> instead of the anonymous object but resulted in a different exception about CategoryId.</p>
  
  <p>Anyone see what I'm missing?</p>