No projects in the migration leads to Cross Project Boards and Filters not getting migrated

Issue Summary

This is reproducible on Data Center: yes

a). When no projects are selected for the migration, the only option available for selecting cross project boards and filters is NONE. 

b). When all the projects in a migration plan are removed from the Pre-migration checks page, the preflight check for cross-project boards and filters get removed too, leading to removal of cross project boards and filters from the migration.

Steps to Reproduce

For a) - 

 1. Skip AR plan and project selections in the Choose your migration Options page
 2. Open the task card for cross-project boards and filters
 3. The only option available is NONE.

For b) - 

 1. Migrate the projects in server
 2. Create a new migration plan with a few project selections.
 3. Choose either All cross-project boards and filters or Only cross-project boards and filters related to selected projects mode.
 4. Click on Run pre-migration checks button
 5. Remove the conflicting projects from the Projects already exist in your cloud site check in the Pre-migration checks screen. (All the selected projects should be removed)
 6. The cross-project boards and filters check vanishes.
 7. On hitting the review migration button, there is no panel for cross project boards and filters.

Workaround

For migration of all cross project boards and filters -  

 1. Select at least one non migrated project or create a dummy project and select it for the migration. 
 2. Choose All cross-project boards and filters option in the Choose your migration options page. (This is presuming the fact that customer wants to migrate all the cross-project boards and filters. If not, see the section below for second workaround).
 3.  Perform the migration.

For migration of selective cross project boards and filters - 

Either delete the projects in cloud which the cross project boards and/or refer to and remigrate the projects along with Only cross-project boards and filters related to selected projects mode.
Or, recreate these cross project boards and/or filters in cloud manually.