Could not resolve placeholder 'guestname' in value "${guestname}" 这个问题怎么解决呢？

2021-06-30 19:18:05.079  INFO 62367 --- [           main] org.example.ClientStartUp                : No active profile set, falling back to default profiles: default

2021-06-30 19:18:07.011  INFO 62367 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=4c86a1f5-12ca-3790-ba18-43cc0ad701de

2021-06-30 19:18:07.224  INFO 62367 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration' of type [org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration$$EnhancerBySpringCGLIB$$300e3331] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

2021-06-30 19:18:07.825  INFO 62367 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 7020 (http)

2021-06-30 19:18:07.850  INFO 62367 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]

2021-06-30 19:18:07.850  INFO 62367 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.31]

2021-06-30 19:18:08.083  INFO 62367 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext

2021-06-30 19:18:08.084  INFO 62367 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 2958 ms

2021-06-30 19:18:08.661  WARN 62367 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testController': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'guestname' in value "${guestname}"

2021-06-30 19:18:08.667  INFO 62367 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]

2021-06-30 19:18:08.711  INFO 62367 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.

2021-06-30 19:18:08.720 ERROR 62367 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testController': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'guestname' in value "${guestname}"

 at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:405) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1422) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:879) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.5.RELEASE.jar:2.2.5.RELEASE]

 at org.example.ClientStartUp.main(ClientStartUp.java:20) ~[classes/:na]

Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'guestname' in value "${guestname}"

 at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:178) ~[spring-core-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:124) ~[spring-core-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:236) ~[spring-core-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:210) ~[spring-core-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.context.support.PropertySourcesPlaceholderConfigurer.lambda$processProperties$0(PropertySourcesPlaceholderConfigurer.java:175) ~[spring-context-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:909) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1228) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1207) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:640) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:130) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399) ~[spring-beans-5.2.4.RELEASE.jar:5.2.4.RELEASE]

 ... 17 common frames omitted

Process finished with exit code 1