If the latest build result does not have a completed date, time based expiry will not run

If the latest build result does not have a completed date, time based expiry will not run.

Steps to replicate

1. Disable all agents
2. Start a plan and watch it go into queue
3. Shutdown Bamboo
4. Restart Bamboo
5. Run a time based expiry (example: expire builds more than 1 day ago)

This message shows up in the log for the tested plan:

 Last build completed date for 'com.atlassian.bamboo.chains.DefaultChain@185ba707:com.atlassian.bamboo.chains.ChainResultsSummaryImpl@c161b50e' is null. No builds will be expired.

Analysis

This behavior is caused by the following code in bamboo/components/bamboo-core/src/main/java/com/atlassian/bamboo/build/expiry/BuildExpiryBeanImpl.java

if (lastBuildDate == null)
           {
               log.warn("Last build completed date for '" + plan + ":" + lastResultsSummary + "' is null. No builds will be expired.");
               return 0;
           }

Workaround

Re-run the build and stop it immediately so that a completed date appears.