title: Spotless gradle plugin not working on closed system
body: <p>I am using gradle 5.4.1. I am using spotless-plugin-gradle 3.25.0.</p>
  
  <p>My build.gradle contains</p>
  
  <pre><code>plugins {
    id 'java'
    id 'eclipse'
    id 'maven-publish'
    id 'com.github.johnrengelman.plugin-shadow' version '2.0.3'
    id 'org.sonarqube' version '2.7.1'
    id 'com.diffplug.gradle.spotless' version '3.25.0'
  }
  </code></pre>
  
  <p>I have spotless in nexus on my closed system (it cannot reach the internet). The gav for spotless in my nexus repository is 'com.diffplug.spotless:spotless-plugin-gradle:3.25.0'.</p>
  
  <p>My settings.gradle file contains:</p>
  
  <pre><code>pluginManagement {
    resolutionStrategy {
      eachPlugin {
        if (requested.id.namespace == "org" &amp;&amp; requested.id.name == "sonarqube") {
          useModule("org.sonarsource.scanner.gradle:sonarqube-gradle-plugin:${requested.version})
        }
        if (requested.id.namespace == "com.github.johnrengelman" &amp;&amp; requested.id.name == "plugin-shadow") {
          useModule("com.github.johnrengelman.gradle.plugins:shadow:${requested.version})
        }
        if (requested.id.namespace == "com.diffplug.gradle" &amp;&amp; requested.id.name == "spotless") {
          useModule("com.diffplug.spotless:spotless-plugin-gradle:${requested.version})
        }
      }
    }
    repositories {
      maven {
        url "http://nexus:8081/repository/jcenter"
      }
    }
  }
  </code></pre>
  
  <p>When I do a "./gradlew dependencies" I get the following error:</p>
  
  <pre><code>An exception occurred applying plugin request [id: 'com.diffplug.gradle.spotless' version: '3.25.0', artifact: 'com.diffplug.spotless:spotless-plugin-gradle:3.25.0']
  &gt; Failed to apply plugin [id: 'com.diffplug.gradle.spotless']
   &gt; Could not create an instance of type com.diffplug.gradle.spotless.SpotlessExtension
    &gt; Could not generate a decorated class for class com.diffplug.gradle.spotless.SpotlessExtension
     &gt; com/diffplug/spotless/LineEnding
  </code></pre>
  
  <p>the stacktrace didn't seem to help much. I tried the old approach (buildscript block) but that results in the same error. Can someone point out what I am doing wrong? On a system where I have direct access to the internet (and thus don't need to add any entries to the settings.gradle file) everything works just fine.</p>