修复代码生成模块中：因手动删除 ruoyi_sys_menu 历史菜单数据不干净，导致点击“上级菜单”出现500的错误

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修复代码生成模块中：因上一次手动删除 ruoyi_sys_menu 历史菜单数据，而该表的“上级菜单”配置修改并未同步清空，再次点击“上级菜单”时出现500的错误。

复现步骤：
1）用户第一次选择目标表并生成对应的代码和菜单SQL（配置了 上级菜单 这一项）， 并且执行菜单SQL完成
2）用户重启服务后发现菜单位置不符合要求，遂删除自动生成的相关代码和菜单SQL，但此时用户并未删除该表的配置信息（尤其是：）
3）用户选择重新生成代码，当点击“上级菜单”这一步时报错，错误如下：

21:10:36.555 [http-nio-10000-exec-25] ERROR o.t.TemplateEngine - [process,1136] - [THYMELEAF][http-nio-10000-exec-25] Exception processing template "system/menu/tree": An error happened during template parsing (template: "class path resource [templates/system/menu/tree.html]") org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/system/menu/tree.html]") at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:241) at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parseStandalone(AbstractMarkupTemplateParser.java:100) …… at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748) Caused by: org.attoparser.ParseException: Exception evaluating SpringEL expression: "menu.menuId" (template: "system/menu/tree" - line 12, col 54) at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:393) at org.attoparser.MarkupParser.parse(MarkupParser.java:257) at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:230) ... 84 common frames omitted Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "menu.menuId" (template: "system/menu/tree" - line 12, col 54) at org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:292) …… at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:301) ... 86 common frames omitted Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1007E: Property or field 'menuId' cannot be found on null at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:219) ……org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator.evaluate(SPELVariableExpressionEvaluator.java:265) ... 105 common frames omitted 21:10:36.744 [http-nio-10000-exec-25] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - [log,175] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/system/menu/tree.html]")] with root cause org.springframework.expression.spel.SpelEvaluationException: EL1007E: Property or field 'menuId' cannot be found on null at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:219) ……

经过分析，发现是点击“上级菜单”时，调用历史设置的菜单ID（2007） 加载后台对应的数据（HTTP接口：system/menu/selectMenuTree/2007 ），而 menuId= 2007 已被手动删除，所以导致SpringEL表达式异常，需要对如下代码做防御性编程：
<input id="treeId" name="treeId" type="hidden" th:value="${menu.menuId}"/> <input id="treeName" name="treeName" type="hidden" th:value="${menu.menuName}"/>