Some problems were encountered while building the effective model for...Maven出现该警告解决方法

Some problems were encountered while building the effective model for cn.itcast:travel:war:1.0-SNAPSHOT
'' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 121, column 21
It is highly recommended to fix these problems because they threaten the stability of your build.
For this reason, future Maven versions might no longer support building such malformed projects.

我这两天开始学习maven，结果发现只有启动，左边一直run个不停不说，完了还出现这种错误，搜了好久，才解决了。原因是f依赖xml配置不全，我是忘记写version
配置

<plugin>
    <groupId></groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.0</version>
    <configuration>
        <source>1.9</source>
        <target>1.9</target>
        <encoding>utf-8</encoding>
    </configuration>
</plugin>