NPE in DefaultContinuum.java - isInBuildingQueue

Not sure what exactly causes this. When the schedule activates, sometimes it would throw this exception and will not proceed with other projects (it will process the one project that it started with, but will not continue on). The problem doesnt happen everytime the schedule activates, but about half of the time. The log is pasted below.

It's the section of code that is throwing the error
for ( Iterator it = queue.iterator(); it.hasNext(); )
{
BuildProjectTask task = (BuildProjectTask) it.next();
............
else
{
if ( task.getProjectId() == projectId && task.getBuildDefinitionId() == buildDefinitionId ) <---- HERE

Log:
jvm 1 | 2007-06-15 14:32:00,426 [defaultScheduler_Worker-1] INFO SchedulesActivator:default - >>>>>>>>>>>>>>>>>>>>> Executing build job (HalfH
ourly)...
jvm 1 | 2007-06-15 14:32:00,574 [defaultScheduler_Worker-1] INFO Continuum:default - Enqueuing 'X12Parser' (Build definition id=7).
jvm 1 | 2007-06-15 14:32:00,575 [pool-1-thread-1] INFO BuildController:default - Initializing build
jvm 1 | 2007-06-15 14:32:00,575 [defaultScheduler_Worker-1] ERROR JobRunShell - Job DEFAULT.HalfHourly threw an unhandled Except
ion:
jvm 1 | java.lang.NullPointerException
jvm 1 | at org.apache.maven.continuum.DefaultContinuum.isInBuildingQueue(DefaultContinuum.java:490)
jvm 1 | at org.apache.maven.continuum.DefaultContinuum.buildProjects(DefaultContinuum.java:843)
jvm 1 | at org.apache.maven.continuum.scheduler.ContinuumBuildJob.execute(ContinuumBuildJob.java:66)
jvm 1 | at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
jvm 1 | at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)
jvm 1 | 2007-06-15 14:32:00,578 [defaultScheduler_Worker-1] ERROR ErrorLogger - Job (DEFAULT.HalfHourly threw an exception.
jvm 1 | org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: java.lang.NullPointerException]
jvm 1 | at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
jvm 1 | at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)
jvm 1 | * Nested Exception (Underlying Cause) ---------------
jvm 1 | java.lang.NullPointerException
jvm 1 | at org.apache.maven.continuum.DefaultContinuum.isInBuildingQueue(DefaultContinuum.java:490)
jvm 1 | at org.apache.maven.continuum.DefaultContinuum.buildProjects(DefaultContinuum.java:843)
jvm 1 | at org.apache.maven.continuum.scheduler.ContinuumBuildJob.execute(ContinuumBuildJob.java:66)
jvm 1 | at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
jvm 1 | at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)
jvm 1 | 2007-06-15 14:32:00,596 [pool-1-thread-1] INFO BuildController:default - Starting build of X12Parser
jvm 1 | 2007-06-15 14:32:00,665 [pool-1-thread-1] INFO BuildController:default - Updating working dir
jvm 1 | 2007-06-15 14:32:00,665 [pool-1-thread-1] INFO BuildController:default - Performing action check-working-directory
jvm 1 | 2007-06-15 14:32:00,666 [pool-1-thread-1] INFO BuildController:default - Performing action update-working-directory-from-scm
jvm 1 | 2007-06-15 14:32:00,709 [pool-1-thread-1] INFO ContinuumScm:default - Updating project: id: '3', name 'X12Parser'.
jvm 1 | 2007-06-15 14:32:00,729 [pool-1-thread-1] INFO ScmManager:default - Executing: svn --non-interactive update
jvm 1 | 2007-06-15 14:32:00,729 [pool-1-thread-1] INFO ScmManager:default - Working directory: C:\buildecosystem\working-directory\3
jvm 1 | 2007-06-15 14:32:01,159 [pool-1-thread-1] INFO BuildController:default - Merging SCM results
jvm 1 | 2007-06-15 14:32:01,166 [pool-1-thread-1] INFO BuildController:default - The project was not built because there are no changes.
jvm 1 | 2007-06-15 14:32:01,168 [pool-1-thread-1] INFO BuildController:default - No changes, not building
jvm 1 | 2007-06-15 15:02:00,046 [defaultScheduler_Worker-5] INFO SchedulesActivator:default - >>>>>>>>>>>>>>>>>>>>> Executing build job (HalfH
ourly)...
jvm 1 | 2007-06-15 15:02:00,190 [defaultScheduler_Worker-5] INFO Continuum:default - Enqueuing 'X12Parser' (Build definition id=7).
jvm 1 | 2007-06-15 15:02:00,191 [defaultScheduler_Worker-5] INFO Continuum:default - Enqueuing 'light-healtheexchange-config' (Build
definition id=7).