fix: 创建测试计划报错

backend/src/main/java/io/metersphere/track/service/TestPlanService.java

@@ -202,12 +202,14 @@ public class TestPlanService {
 
         String planId = testPlan.getId();
         List<String> principals = testPlan.getPrincipals();
+        if (!CollectionUtils.isEmpty(principals)) {
             for (String principal : principals) {
                 TestPlanPrincipal testPlanPrincipal = new TestPlanPrincipal();
                 testPlanPrincipal.setTestPlanId(planId);
                 testPlanPrincipal.setPrincipalId(principal);
                 testPlanPrincipalService.insert(testPlanPrincipal);
             }
+        }
 
         if (StringUtils.isBlank(testPlan.getProjectId())) {
             testPlan.setProjectId(SessionUtils.getCurrentProjectId());