SampleResult: sampleEnd called twice

[Ronghefeng]

When I use the plug-in to call the interface, this error occurs most often, sometimes it is correct, what is the reason for this？
error info：
2021-05-17 16:45:18,702 INFO o.a.j.e.StandardJMeterEngine: Running the test!
2021-05-17 16:45:18,702 INFO o.a.j.s.SampleEvent: List of sample_variables: []
2021-05-17 16:45:18,704 INFO o.a.j.g.u.JMeterMenuBar: setRunning(true, local)
2021-05-17 16:45:18,776 INFO o.a.j.e.StandardJMeterEngine: Starting ThreadGroup: 1 : Thread Group
2021-05-17 16:45:18,776 INFO o.a.j.e.StandardJMeterEngine: Starting 1 threads for group Thread Group.
2021-05-17 16:45:18,776 INFO o.a.j.e.StandardJMeterEngine: Thread will continue on error
2021-05-17 16:45:18,777 INFO o.a.j.t.ThreadGroup: Starting thread group... number=1 threads=1 ramp-up=1 delayedStart=false
2021-05-17 16:45:18,777 INFO o.a.j.t.ThreadGroup: Started thread group number 1
2021-05-17 16:45:18,778 INFO o.a.j.e.StandardJMeterEngine: All thread groups have been started
2021-05-17 16:45:18,779 INFO o.a.j.t.JMeterThread: Thread started: Thread Group 1-1
2021-05-17 16:45:18,781 INFO v.z.b.GRPCSampler: Thread Group 1-1@53aaa435-GRPC Request testStarted
2021-05-17 16:45:19,296 ERROR o.a.j.s.SampleResult: sampleEnd called twice
java.lang.Throwable: Invalid call sequence
at org.apache.jmeter.samplers.SampleResult.sampleEnd(SampleResult.java:1147) [ApacheJMeter_core.jar:5.4.1]
at vn.zalopay.benchmark.GRPCSampler.errorResult(GRPCSampler.java:126) [jmeter-grpc-request-1.1.2.jar:?]
at vn.zalopay.benchmark.GRPCSampler.sample(GRPCSampler.java:86) [jmeter-grpc-request-1.1.2.jar:?]
at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:638) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:558) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:489) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:256) [ApacheJMeter_core.jar:5.4.1]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_291]
2021-05-17 16:45:19,297 ERROR o.a.j.s.SampleResult: sampleEnd called twice
java.lang.Throwable: Invalid call sequence
at org.apache.jmeter.samplers.SampleResult.sampleEnd(SampleResult.java:1147) [ApacheJMeter_core.jar:5.4.1]
at vn.zalopay.benchmark.GRPCSampler.errorResult(GRPCSampler.java:126) [jmeter-grpc-request-1.1.2.jar:?]
at vn.zalopay.benchmark.GRPCSampler.sample(GRPCSampler.java:89) [jmeter-grpc-request-1.1.2.jar:?]
at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:638) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:558) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:489) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:256) [ApacheJMeter_core.jar:5.4.1]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_291]
2021-05-17 16:45:19,297 ERROR o.a.j.t.JMeterThread: Error while processing sampler: 'GRPC Request'.
java.lang.NullPointerException: null
at vn.zalopay.benchmark.GRPCSampler.errorResult(GRPCSampler.java:128) ~[jmeter-grpc-request-1.1.2.jar:?]
at vn.zalopay.benchmark.GRPCSampler.sample(GRPCSampler.java:89) ~[jmeter-grpc-request-1.1.2.jar:?]
at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:638) ~[ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:558) ~[ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:489) [ApacheJMeter_core.jar:5.4.1]
at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:256) [ApacheJMeter_core.jar:5.4.1]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_291]
2021-05-17 16:45:19,297 INFO o.a.j.t.JMeterThread: Thread is done: Thread Group 1-1
2021-05-17 16:45:19,297 INFO o.a.j.t.JMeterThread: Thread finished: Thread Group 1-1
2021-05-17 16:45:19,297 INFO v.z.b.GRPCSampler: Thread Group 1-1@53aaa435-GRPC Request testEnded
2021-05-17 16:45:19,298 INFO o.a.j.e.StandardJMeterEngine: Notifying test listeners of end of test
2021-05-17 16:45:19,298 INFO o.a.j.g.u.JMeterMenuBar: setRunning(false, local)