Heroku buildback未检测到根项目Spring Boot中未找到java任务“stage”

Question

由于日志中出现以下错误，我无法在Heroku部署Spring Boot应用程序：

   FAILURE: Build failed with an exception.

   * What went wrong:
   Task 'stage' not found in root project 'scraper'.

   * Try:
   Run gradlew tasks to get a list of available tasks. Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

从the docs：

The Gradle buildpack will run different build tasks depending on the frameworks it detects in your app. For Spring Boot, it will run ./gradlew build -x test. For Ratpack, it will run ./gradlew installDist -x test. If no known web frameworks are detected, it will run ./gradlew stage.

这意味着Heroku没有检测到Spring Boot，而是作为通用框架运行。。问题是为什么。在日志的开头，我得到：

-----> Gradle app detected
-----> Installing JDK 1.8... done
-----> Building Gradle app...
-----> executing ./gradlew stage

作为技术人员，我有Spring Boot 2.1.1、Gradle和Kotlin 1.3.11

谢谢