Issue Summary

This is reproducible on Data Center:

While trying to perform an attachments-only migration from the source Confluence Server/Data Center instance to the destination cloud site using CCMA 3.9.11, the execution of the migration plan fails after a few seconds:

Steps to Reproduce

1. Create a migration plan in CCMA.
2. In the Spaces section, select the Attachments only option.
3. Run that migration plan.

Expected Results

The attachments from the selected spaces are successfully migrated over.

Actual Results

The execution of the migration plan fails after a few seconds with the following error message:

We couldn't complete the migration. Review the error log and then run a new migration.

The following ERROR is thrown in the attlassian-confluence-migrations.log file:

<date_time> ERROR [com.atlassian.migration.agent.service.impl.PlanDecoratorService:<thread_number>] [agent.service.impl.DefaultPlanService] startPlan Fail to start the plan: <plan_ID>
 -- url: /confluence/rest/migration/latest/plan/<plan_ID>/start | userName: <user_name> | referer: <base_URL>/confluence/admin/migration.action | traceId: <trace_ID>
java.lang.NullPointerException: Cannot invoke "java.util.List.stream()" because the return value of "java.util.Map.get(Object)" is null

Workaround

1. Upgrade CCMA to version 3.9.12 or higher (preferably the latest version).
2. Clear the Confluence plugins cache.
3. Create a new migration plan in CCMA.
4. In the Spaces section, select the Attachments only option.
5. Run that new migration plan.