title: Operator called default onErrorDropped after upgrading the Spring boot version from 2.1.7 to 2.6.4
body: <p>This code is running fine in <strong>Springboot 2.1.7</strong> version but after upgrading it to <strong>Springboot 2.6.4</strong> it throws exception. Unable to rectify the issue. Let me know where I have to change in code</p>
  <pre><code> fun getScheduledTasks(): Flux&lt;*&gt; {
          return Flux.fromIterable(tasks)
                  .filter {
                      logger.info(&quot;{} was enabled? {}&quot;, it::class.qualifiedName, it.config.enabled)
                      it.config.enabled
                  }
                  .flatMap { task -&gt;
                      Flux.interval(task.config.initialDelay, task.config.interval)
                              .flatMap {
                                  logger.info(&quot;Beginning task &quot;)
                                  task.execute()
                                      .doOnNext {
                                          logger.info(&quot;Completed task {}&quot;, task::class.qualifiedName)
                                      }
                                      .onErrorResume { err -&gt;
                                          logger.warn(“Error in running {}.&quot;, task::class.qualifiedName, err)
                                          Mono.empty()
                                      }
                              }
                              .doFinally {
                                  logger.warn(“Taskcompleted unexpectedly: {}&quot;, it.name)
                              }
                  }
      }
  </code></pre>
  <p><strong>Exception:</strong></p>
  <pre><code>2022-07-18 12:05:49.649  INFO 5440 --- [     parallel-1] c.u.cpp.background.runner.Runner         : Beginning  task 
  2022-07-18 12:05:49.657 ERROR 5440 --- [ntLoopGroup-3-5] reactor.core.publisher.Operators         : Operator called default onErrorDropped
  
  reactor.core.Exceptions$ErrorCallbackNotImplemented: java.lang.NullPointerException: t is null in sink.next(t)
  Caused by: java.lang.NullPointerException: t is null in sink.next(t)
      at java.util.Objects.requireNonNull(Objects.java:228)
      at reactor.core.publisher.FluxCreate$SerializedFluxSink.next(FluxCreate.java:147)
      at com.mongodb.reactivestreams.client.internal.BatchCursorFlux$$Lambda$1536/0x0000000067460320.accept(Unknown Source)
      at java.util.ArrayList.forEach(ArrayList.java:1259)
      at com.mongodb.reactivestreams.client.internal.BatchCursorFlux.lambda$recurseCursor$4(BatchCursorFlux.java:94)
      at com.mongodb.reactivestreams.client.internal.BatchCursorFlux$$Lambda$1535/0x0000000067d52a20.accept(Unknown Source)
      at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:171)
      at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:180)
      at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:854)
      at reactor.core.publisher.MonoCreate$DefaultMonoSink.success(MonoCreate.java:165)
      at
  </code></pre>