我按照本指南开发了自己的（非常简单）自定义 Maven 插件。
它所做的只是在运行特定目标后执行我自己项目的主类。
当我在插件上运行 mvn install 时，我得到了NullPointerExceptionmaven-plugin-plugin:descriptor 目标。值得一提的是，如果我使用<systemPath>绝对路径添加依赖项并添加<scope>system</scope>选项，则不会发生这种情况。
堆栈跟踪：
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:3.2:descriptor (default-descriptor) on project gentest-maven-plugin: Execution default-descriptor of goal org.apache.maven.plugins:maven-plugin-plugin:3.2:descriptor failed.: NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:3.2:descriptor (default-descriptor) on project gentest-maven-plugin: Execution default-descriptor of goal org.apache.maven.plugins:maven-plugin-plugin:3.2:descriptor failed.
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:213)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
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:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:309)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:194) …