Why Does “org.apache.flink.client.deployment.application.ApplicationExecutionException: The application contains no execute() calls” Occur When I Change the Processing Function of a Flink Task from KeyedProcessFunction to KeyedCoProcessFunction?

The error log is as follows:

java.util.concurrent.CompletionException: org.apache.flink.client.deployment.application.ApplicationExecutionException: The application contains no execute() calls.
at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:292) ~[?:1.8.0_402]
at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:308) ~[?:1.8.0_402]
at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:957) ~[?:1.8.0_402]
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:940) ~[?:1.8.0_402]
at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:488) ~[?:1.8.0_402]
at java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:1990) ~[?:1.8.0_402]
at org.apache.flink.client.deployment.application.ApplicationDispatcherBootstrap.runApplicationEntryPoint(ApplicationDispatcherBootstrap.java:385) ~[flink-dist-1.17.1-h3.xxx.jar:1.17.1-h3.xxx]
at org.apache.flink.client.deployment.application.ApplicationDispatcherBootstrap.lambda$runApplicationAsync$3(ApplicationDispatcherBootstrap.java:303) ~[flink-dist-1.17.1-h3.xxx.jar:1.17.1-h3.xxx]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_402]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_402]
at org.apache.flink.runtime.concurrent.akka.ActorSystemScheduledExecutorAdapter$ScheduledFutureTask.run(ActorSystemScheduledExecutorAdapter.java:171) ~[flink-rpc-akka_9c16cc6a-e7af-4810-9573-6a1dc248ae52.jar:1.17.1-h3.xxx]
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.runWithContextClassLoader(ClassLoadingUtils.java:68) ~[flink-rpc-akka_9c16cc6a-e7af-4810-9573-6a1dc248ae52.jar:1.17.1-h3.xxx]
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.lambda$withContextClassLoader$0(ClassLoadingUtils.java:41) ~[flink-rpc-akka_9c16cc6a-e7af-4810-9573-6a1dc248ae52.jar:1.17.1-h3.xxx]
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:49) [flink-rpc-akka_9c16cc6a-e7af-4810-9573-6a1dc248ae52.jar:1.17.1-h3.xxx]
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:48) [flink-rpc-akka_9c16cc6a-e7af-4810-9573-6a1dc248ae52.jar:1.17.1-h3.xxx]
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289) [?:1.8.0_402]
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056) [?:1.8.0_402]
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692) [?:1.8.0_402]
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:175) [?:1.8.0_402]
Caused by: org.apache.flink.client.deployment.application.ApplicationExecutionException: The application contains no execute() calls.
… 13 more

I don‘t know how to deal with this problem, i do nothing.