When using xa enlistment (transaction/useSynchronization=false, default), and recovery is disabled (transaction/recovery/enabled=false, default) the transaction manager might invoke recovery related methods such as XAResource.forget() in certain situations.
E.g. the JBossTM invokes "forget", if during, XAResource.commit(xid, true) (second param means 1PC=true) an exception is thrown. (I expect an XAResource.rollback to be invoked in between the failed commit and forget).
Here is such a stack trace:

2012-07-25 14:13:42,821 WARN (testng-CheckRemoteLockAcquiredOnlyOnceDistTest [org.infinispan.transaction.xa.TransactionXaAdapter] Exception removing recovery information:java.lang.NullPointerException
at org.infinispan.transaction.xa.TransactionXaAdapter.forget(TransactionXaAdapter.java:159)
at com.arjuna.ats.internal.jta.resources.arjunacore.XAResourceRecord.forget(XAResourceRecord.java:759)
at com.arjuna.ats.internal.jta.resources.arjunacore.XAResourceRecord.topLevelOnePhaseCommit(XAResourceRecord.java:691)
at com.arjuna.ats.arjuna.coordinator.BasicAction.onePhaseCommit(BasicAction.java:2285)
at com.arjuna.ats.arjuna.coordinator.BasicAction.End(BasicAction.java:1468)
at com.arjuna.ats.arjuna.coordinator.TwoPhaseCoordinator.end(TwoPhaseCoordinator.java:98)
at com.arjuna.ats.arjuna.AtomicAction.commit(AtomicAction.java:164)
at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.commitAndDisassociate(TransactionImple.java:1165)
at com.arjuna.ats.internal.jta.transaction.arjunacore.BaseTransaction.commit(BaseTransaction.java:117)
at org.infinispan.lock.CheckRemoteLockAcquiredOnlyOnceTest.testLockThenOperation(CheckRemoteLockAcquiredOnlyOnceTest.java:157)
at org.infinispan.lock.CheckRemoteLockAcquiredOnlyOnceTest.testLockThenPutAll(CheckRemoteLockAcquiredOnlyOnceTest.java:100)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:74)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:673)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:846)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1170)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:125)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:109)
at org.testng.TestRunner.runWorkers(TestRunner.java:1147)
at org.testng.TestRunner.privateRun(TestRunner.java:749)
at org.testng.TestRunner.run(TestRunner.java:600)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:317)
at org.testng.SuiteRunner.access$000(SuiteRunner.java:34)
at org.testng.SuiteRunner$SuiteWorker.run(SuiteRunner.java:351)
at org.testng.internal.thread.ThreadUtil$CountDownLatchedRunnable.run(ThreadUtil.java:147)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)

As we do allow xa enlistment without recovery enabled this NPE shouldn't be shown to the user.
Instead an warning should be logged stating that XA enlistment is configured without recovery, but recovery might be needed in certain situations.