title: Maven enforcer plugin missing or invalid rules
body: <p>I am trying to setup the enforcer plugin for maven to enforce a minimum Java version. However, whenever I try to run <code>mvn enforcer:enforce</code>, I get:</p>
  
  <blockquote>
    <p>The parameters 'rules' for goal org.apache.maven.plugins:maven-enforcer-plugin:1.3.1:enforce are missing or invalid</p>
  </blockquote>
  
  <p>Here is the relevant portion of my pom file:</p>
  
  <pre><code>&lt;plugin&gt;
      &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
      &lt;artifactId&gt;maven-enforcer-plugin&lt;/artifactId&gt;
      &lt;version&gt;1.3.1&lt;/version&gt;
      &lt;executions&gt;
          &lt;execution&gt;
              &lt;id&gt;enforce-java&lt;/id&gt;
              &lt;phase&gt;validate&lt;/phase&gt;
              &lt;goals&gt;
                  &lt;goal&gt;enforce&lt;/goal&gt;
              &lt;/goals&gt;
              &lt;configuration&gt;
                  &lt;rules&gt;
                      &lt;requireJavaVersion&gt;
                          &lt;version&gt;(1.7.0-20,)&lt;/version&gt;
                      &lt;/requireJavaVersion&gt;
                  &lt;/rules&gt;
              &lt;/configuration&gt;
          &lt;/execution&gt;
      &lt;/executions&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p>I also tried replacing the <code>&lt;requireJavaVersion&gt;</code> block with <code>&lt;alwaysPass/&gt;</code>, in case something was invalid, but it still failed with the same error.</p>