Google App Engine上的Spring Boot应用程序：无法找到主类

我有一个在GCP上运行的Spring Boot应用程序（至今已有1年），我想对其进行更新，但是在mvn appengine:run本地运行时出现此错误：

[INFO] GCLOUD: INFOS: javax.servlet.ServletContext log: 2 Spring WebApplicationInitializers detected on classpath
[INFO] GCLOUD: java.lang.IllegalArgumentException: Unable to find the main class to restart
[INFO] GCLOUD:  at org.springframework.util.Assert.notNull(Assert.java:198)
[INFO] GCLOUD:  at org.springframework.boot.devtools.restart.Restarter.doStart(Restarter.java:277)
[INFO] GCLOUD:  at org.springframework.boot.devtools.restart.Restarter.start(Restarter.java:265)
[INFO] GCLOUD:  at org.springframework.boot.devtools.restart.Restarter.lambda$immediateRestart$0(Restarter.java:173)
[INFO] GCLOUD:  at org.springframework.boot.devtools.restart.Restarter$LeakSafeThread.run(Restarter.java:637)
[INFO] GCLOUD: d?c. 02, 2018 4:30:20 PM com.google.appengine.api.datastore.dev.LocalDatastoreService cleanupActiveServices
[INFO] GCLOUD: INFOS: scheduler shutting down.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  53.255 s
[INFO] Finished at: 2018-12-02T17:30:21+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.google.cloud.tools:appengine-maven-plugin:1.3.1:run (default-cli) on project sample-app: Execution default-cli of goal com.google.cloud.tools:appengine-maven-plugin:1.3.1:run failed: Non zero exit: 1 -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.google.cloud.tools:appengine-maven-plugin:1.3.1:run (default-cli) on project tacos-time29: Execution default-cli of goal com.google.cloud.tools:appengine-maven-plugin:1.3.1:run failed: Non zero exit: 1
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)

主类有问题。在我的pom.xm中，我定义了以下内容：

<properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <appengine.maven.plugin>1.3.1</appengine.maven.plugin>
    <!--Definition of the main class-->
    <start-class>com.example.sample.Application</start-class>
</properties>

我还在spring-boot-plugin中定义了主类

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <mainClass>${start-class}</mainClass>
    </configuration>
</plugin>

并且/WEB-INF/appengine-web.xml文件的内容是基本的：

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <version>1</version>
    <threadsafe>true</threadsafe>
    <runtime>java8</runtime>
</appengine-web-app>

谢谢你的帮助