Potential NPE when logging long-running tasks

In the ThreadUtils class, we have the following code:

if (monitor.getLockedStackFrame().equals(element))

 However, getLockedStackFrame() can return null, which results in a NPE such as:
2021-10-24 11:38:17,122 ERROR org.apache.nifi.engine.FlowEngine: Uncaught Exception in Runnable task
java.lang.NullPointerException: null
at org.apache.nifi.util.ThreadUtils.createStackTrace(ThreadUtils.java:72)
at org.apache.nifi.controller.StandardProcessorNode.getActiveThreads(StandardProcessorNode.java:1443)
at org.apache.nifi.components.monitor.LongRunningTaskMonitor.run(LongRunningTaskMonitor.java:57)
at org.apache.nifi.engine.FlowEngine$2.run(FlowEngine.java:110)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)