Crash add new related many-to-many item

[racke]

Add existing related item works.

The related class has an autoincrement primary key and a name field. TableEditor tries
to insert the following:

Updating item for ResourceSection: {'values' => {'name' => 'Bah','null' => '69'}}

This crashes as null isn't a column.

Creating a ResourceSection item directly works:

Updating item for ResourceSection: {'values' => {'name' => 'Show and Go'}}