While setting up your SharePoint Framework (SPFx) Preview Environment, you receive ‘ClientSideApplicationId’ does not exists in list or list item

In order to develop new client-side web parts using the SharePoint Framework (SPFx) preview, you will need the following correctly setup:

1. An Office 365 Developer Tenant (note that it must be a developer tenant via the Office Dev Program)
2. A working App Catalog site in your tenant
3. A developer site collection
4. An uploaded workbench.aspx file to the library
5. A site column in your “Documents” document library called “ClientSideApplicationId“

If you try to browse to your site (i.e. https://mytenant.sharepoint.com/sites/dev/Shared%20Documents/workbench.aspx) and miss or forget step #5 , you will get the following error:

‘ClientSideApplicationId’ does not exists in list or list item

All of these instructions can be found here.