[Bug] [Task] A single task instance runs or runs backwards only once

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/dolphinscheduler/issues?q=is%3Aissue) and found no similar issues.

### What happened

A single task instance runs or runs backwards only once
```
[WI-0][TI-0] - [ERROR] 2025-02-06 15:57:45.452 +0800 o.a.d.s.m.r.MasterSchedulerBootstrap:[153] - Master handle command 1160 error
org.apache.dolphinscheduler.server.master.exception.WorkflowCreateException: Create WorkflowExecuteRunnable failed
at org.apache.dolphinscheduler.server.master.runner.WorkflowExecuteRunnableFactory.createWorkflowExecuteRunnable(WorkflowExecuteRunnableFactory.java:98)
at org.apache.dolphinscheduler.server.master.runner.MasterSchedulerBootstrap.lambda$run$0(MasterSchedulerBootstrap.java:136)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1384)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinTask.doInvoke(ForkJoinTask.java:401)
at java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:734)
at java.util.stream.ForEachOps$ForEachOp.evaluateParallel(ForEachOps.java:160)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(ForEachOps.java:174)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:583)
at org.apache.dolphinscheduler.server.master.runner.MasterSchedulerBootstrap.run(MasterSchedulerBootstrap.java:133)
Caused by: java.lang.NullPointerException: null
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:889)
at com.google.common.collect.Lists.newArrayList(Lists.java:128)
at org.apache.dolphinscheduler.service.process.ProcessServiceImpl.joinVarPool(ProcessServiceImpl.java:1038)
at org.apache.dolphinscheduler.service.process.ProcessServiceImpl.setSubProcessParam(ProcessServiceImpl.java:982)
at org.apache.dolphinscheduler.service.process.ProcessServiceImpl.handleCommand(ProcessServiceImpl.java:316)
at org.apache.dolphinscheduler.service.process.ProcessServiceImpl$$FastClassBySpringCGLIB$$9d3e18f9.invoke()
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:793)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708)
at org.apache.dolphinscheduler.service.process.ProcessServiceImpl$$EnhancerBySpringCGLIB$$6edc3705.handleCommand()
at org.apache.dolphinscheduler.server.master.runner.WorkflowExecuteContextFactory.createWorkflowInstance(WorkflowExecuteContextFactory.java:81)
at org.apache.dolphinscheduler.server.master.runner.WorkflowExecuteContextFactory.createWorkflowExecuteRunnableContext(WorkflowExecuteContextFactory.java:56)
at org.apache.dolphinscheduler.server.master.runner.WorkflowExecuteRunnableFactory.createWorkflowExecuteRunnable(WorkflowExecuteRunnableFactory.java:83)
... 15 common frames omitted
```

### What you expected to happen
https://github.com/apache/dolphinscheduler/blob/8ee334fc2f4803d7a628458018d82ca695b920d1/dolphinscheduler-task-plugin/dolphinscheduler-task-api/src/main/java/org/apache/dolphinscheduler/plugin/task/api/utils/VarPoolUtils.java#L97

An empty array should be returned here, not null. However, the unit test specifies null. I don't know what it means.
```
@Test
void subtractVarPool() {
Truth.assertThat(VarPoolUtils.subtractVarPool(null, null)).isNull();
List varpool1 = Lists.newArrayList(new Property("name", Direct.OUT, DataType.VARCHAR, "tom"),
new Property("age", Direct.OUT, DataType.INTEGER, "10"));
List varpool2 = Lists.newArrayList(new Property("name", Direct.OUT, DataType.VARCHAR, "tom"));
List varpool3 = Lists.newArrayList(new Property("location", Direct.OUT, DataType.VARCHAR, "china"));

Truth.assertThat(VarPoolUtils.subtractVarPool(varpool1, Lists.newArrayList(varpool2, varpool3)))
.containsExactly(new Property("age", Direct.OUT, DataType.INTEGER, "10"));
}
```


### How to reproduce

Process logic: A workflow is nested in another workflow through the sub_process method
- Main workflow logic


- Sub-workflow logic


Problem: When the run fails.


Enter the workflow instance



Execute backwards, or run can only be executed successfully once. No response will occur if executed again.
### Anything else

_No response_

### Version

3.2.x

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)