'build.plugins.plugin.version' for com.pyx4me:proguard-maven-plugin is missing. @ line 42, column 12

‘build.plugins.plugin.version’ for com.pyx4me:proguard-maven-plugin is missing. @ line 42, column 12

执行Maven Install的时候提示如下警告信息：

[WARNING] 
[WARNING] Some problems were encountered while building the effective model for xunge-middleware:xunge-middleware:war:0.0.1-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for com.pyx4me:proguard-maven-plugin is missing. @ line 42, column 12 [WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]

其实警告信息忽略不管也可以的，不过这里的警告是关于插件版本的，最好还是指定版本：

<plugin> <groupId>com.pyx4megroupId> <artifactId>proguard-maven-pluginartifactId> **<version>2.0.4version>** <executions> <execution> <phase>packagephase> <goals> <goal>proguardgoal> goals> execution> executions> <configuration> <obfuscate>trueobfuscate> <proguardInclude>${basedir}/proguard.confproguardInclude>  <libs> <lib>${java.home}/lib/rt.jarlib> <lib>lib/jsp-api.jarlib> <lib>lib/servlet-api.jarlib> libs> <addMavenDescriptor>falseaddMavenDescriptor> configuration> <dependencies>  <dependency> <groupId>net.sf.proguardgroupId> <artifactId>proguardartifactId> <version>4.8version> <scope>runtimescope> dependency> dependencies> plugin>

添加了2.0.4警告就消失了。