【缺陷修复】 流程预测时，不能计算流程表达式时，返回空列表，避免流程无法进行下去

yudao-module-bpm/yudao-module-bpm-biz/src/main/java/cn/iocoder/yudao/module/bpm/framework/flowable/core/candidate/strategy/other/BpmTaskCandidateExpressionStrategy.java

@@ -4,10 +4,14 @@ import cn.hutool.core.convert.Convert;
 import cn.iocoder.yudao.module.bpm.framework.flowable.core.candidate.BpmTaskCandidateStrategy;
 import cn.iocoder.yudao.module.bpm.framework.flowable.core.enums.BpmTaskCandidateStrategyEnum;
 import cn.iocoder.yudao.module.bpm.framework.flowable.core.util.FlowableUtils;
+import com.google.common.collect.Sets;
+import lombok.extern.slf4j.Slf4j;
 import org.flowable.bpmn.model.BpmnModel;
+import org.flowable.common.engine.api.FlowableException;
 import org.flowable.engine.delegate.DelegateExecution;
 import org.springframework.stereotype.Component;
 
+import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 
@@ -17,6 +21,7 @@ import java.util.Set;
  * @author 芋道源码
  */
 @Component
+@Slf4j
 public class BpmTaskCandidateExpressionStrategy implements BpmTaskCandidateStrategy {
 
     @Override
@@ -38,8 +43,16 @@ public class BpmTaskCandidateExpressionStrategy implements BpmTaskCandidateStrat
     @Override
     public Set<Long> calculateUsersByActivity(BpmnModel bpmnModel, String activityId, String param,
                                               Long startUserId, String processDefinitionId, Map<String, Object> processVariables) {
-        Object result = FlowableUtils.getExpressionValue(processVariables, param);
-        return Convert.toSet(Long.class, result);
+        Map<String, Object> variables = processVariables == null ? new HashMap<>() : processVariables;
+        try {
+            Object result = FlowableUtils.getExpressionValue(variables, param);
+            return Convert.toSet(Long.class, result);
+        } catch (FlowableException ex) {
+            // 预测未运行的节点时候，表达式如果包含 execution 或者不存在的流程变量会抛异常，
+            log.warn("[calculateUsersByActivity][表达式({}) 变量({}) 解析报错", param, variables, ex);
+            // 不能预测候选人，返回空列表, 避免流程无法进行
+            return Sets.newHashSet();
+        }
     }
 
 }