update(REQ-2324) - 解决设置审批人如果为空，则自动驳回

workflow-engine-core/src/main/java/cn/axzo/workflow/core/service/impl/BpmnProcessActivityServiceImpl.java

@@ -45,6 +45,9 @@ public class BpmnProcessActivityServiceImpl implements BpmnProcessActivityServic
         CommandExecutor commandExecutor = processEngineConfiguration.getCommandExecutor();
         if (CollectionUtils.isEmpty(dto.getAssigners())) {
             Execution execution = runtimeService.createExecutionQuery().executionId(dto.getTriggerId()).singleResult();
+            if (Objects.isNull(execution)) {
+                throw new WorkflowEngineException(ACTIVITY_TRIGGER_NOT_EXISTS, dto.getTriggerId());
+            }
             commandExecutor.execute(new CustomAbortProcessInstanceCmd(execution.getProcessInstanceId(), null, "业务未指定审批人", extAxHiTaskInstService));
             return;
         }