NPE when closing UnboundedSourceWrapper

2020-07-16 14:51:00,282 ERROR org.apache.flink.streaming.runtime.tasks.StreamTask - Error during disposal of stream operator.
java.lang.NullPointerException
at org.apache.beam.runners.flink.translation.wrappers.streaming.io.UnboundedSourceWrapper.close(UnboundedSourceWrapper.java:351)
at org.apache.flink.api.common.functions.util.FunctionUtils.closeFunction(FunctionUtils.java:43)
at org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.dispose(AbstractUdfStreamOperator.java:117)
at org.apache.flink.streaming.runtime.tasks.StreamTask.disposeAllOperators(StreamTask.java:651)
at org.apache.flink.streaming.runtime.tasks.StreamTask.cleanUpInvoke(StreamTask.java:562)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:480)
at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:708)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:533)
at java.lang.Thread.run(Thread.java:748)