fix：【BPM 工作流】bpmn subProcess 存在 userTask NPE 的问题

yudao-module-bpm/src/main/java/cn/iocoder/yudao/module/bpm/framework/flowable/core/candidate/BpmTaskCandidateInvoker.java

@@ -18,10 +18,7 @@ import cn.iocoder.yudao.module.system.api.user.AdminUserApi;
 import cn.iocoder.yudao.module.system.api.user.dto.AdminUserRespDTO;
 import com.google.common.annotations.VisibleForTesting;
 import lombok.extern.slf4j.Slf4j;
-import org.flowable.bpmn.model.BpmnModel;
-import org.flowable.bpmn.model.CallActivity;
-import org.flowable.bpmn.model.FlowElement;
-import org.flowable.bpmn.model.UserTask;
+import org.flowable.bpmn.model.*;
 import org.flowable.engine.delegate.DelegateExecution;
 import org.flowable.engine.runtime.ProcessInstance;
 
@@ -132,7 +129,7 @@ public class BpmTaskCandidateInvoker {
                                               Long startUserId, String processDefinitionId, Map<String, Object> processVariables) {
         // 如果是 CallActivity 子流程，不进行计算候选人
         FlowElement flowElement = BpmnModelUtils.getFlowElementById(bpmnModel, activityId);
-        if (flowElement instanceof CallActivity) {
+        if (flowElement instanceof CallActivity || flowElement instanceof SubProcess) {
             return new HashSet<>();
         }
         // 审批类型非人工审核时，不进行计算候选人。原因是：后续会自动通过、不通过

yudao-module-bpm/src/main/java/cn/iocoder/yudao/module/bpm/framework/flowable/core/util/BpmnModelUtils.java

@@ -478,7 +478,11 @@ public class BpmnModelUtils {
      */
     public static FlowElement getFlowElementById(BpmnModel model, String flowElementId) {
         Process process = model.getMainProcess();
-        return process.getFlowElement(flowElementId);
+        FlowElement flowElement = process.getFlowElement(flowElementId);
+        if (flowElement != null) {
+            return flowElement;
+        }
+        return model.getFlowElement(flowElementId);
     }
 
     /**

yudao-module-bpm/src/main/java/cn/iocoder/yudao/module/bpm/service/task/BpmTaskServiceImpl.java

@@ -1379,7 +1379,7 @@ public class BpmTaskServiceImpl implements BpmTaskService {
                         PROCESS_INSTANCE_VARIABLE_SKIP_START_USER_NODE, String.class));
                 if (userTaskElement.getId().equals(START_USER_NODE_ID)
                         && (skipStartUserNodeFlag == null // 目的：一般是“主流程”，发起人节点，自动通过审核
-                        || Boolean.TRUE.equals(skipStartUserNodeFlag)) // 目的：一般是“子流程”，发起人节点，按配置自动通过审核
+                            || BooleanUtil.isTrue(skipStartUserNodeFlag)) // 目的：一般是“子流程”，发起人节点，按配置自动通过审核
                         && ObjUtil.notEqual(returnTaskFlag, Boolean.TRUE)) {
                     getSelf().approveTask(Long.valueOf(task.getAssignee()), new BpmTaskApproveReqVO().setId(task.getId())
                             .setReason(BpmReasonEnum.ASSIGN_START_USER_APPROVE_WHEN_SKIP_START_USER_NODE.getReason()));