!780 fix: 修复CompleteTaskDTO中getVariables()中variables == null 时的返回值问题

* fix: 修复CompleteTaskDTO中getVariables()中variables == null 时的返回值问题

ruoyi-common/ruoyi-common-core/src/main/java/org/dromara/common/core/domain/dto/CompleteTaskDTO.java

@@ -67,7 +67,8 @@ public class CompleteTaskDTO implements Serializable {
 
     public Map<String, Object> getVariables() {
         if (variables == null) {
-            return new HashMap<>(16);
+            variables = new HashMap<>(16);
+            return variables;
         }
         variables.entrySet().removeIf(entry -> Objects.isNull(entry.getValue()));
         return variables;