Issue Summary

When work items are moved from an active process step to Unassigned in Backlog - Kanban - Process Flow view, the ProcessStepID is set to 0, which is an invalid step. Efforts to PATCH the work item will then result in an invalid ProcessStepID error because ProcessStepID is not included in the Process Flow.

Steps to Reproduce

1. Apply a Process Flow
2. Navigate to Backlog > Capabilities Backlog > Kanban - Process Flow View
3. Move the Capability to any Process Step other than Unassigned in the Backlog
4. Move the Capability back to Unassigned
5. GET on the Capability will return 0 for processStepId field
6. PATCH on the Capability for any field returns invalid processStepId error

Expected Results

Process Step ID 0 is excluded from API validations

Actual Results

API PATCH calls fail with processStepId = 0 because that step cannot be included in any Process Flow

Workaround

Move the work item to any other Process Step in the Kanban view, or assign it a Process Step in the Details tab.