有人可以帮我解决切入点。如何找到根本原因？复制下面的堆栈跟踪：
[workspace] $ /usr/atria/bin/cleartool catcs -tag XXXXX
element * CHECKEDOUT
element * .../XXXXsupport_2.2/LATEST
element * /main/LATEST -mkbranch XXXXsupport_2.2
load /vobs/XXXX
java.io.IOException: Failed to parse changelog
at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild>.java:622)
at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:86)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:529)
at hudson.model.Run.execute(Run.java:1741)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:98)
at hudson.model.Executor.run(Executor.java:410)
Caused by: java.lang.NullPointerException
Discard old builds...