title: Invalid publication 'mavenJava': multiple artifacts with the identical extension and classifier
body: <p>I have multiple ZIP artifacts that I would like to publish with the same artifact ID using maven-publish Gradle (kts) plugin but I keep getting the error:</p>
  <pre><code>Execution failed for task ':publishMavenJavaPublicationToMavenLocal'.
  &gt; Failed to publish publication 'mavenJava' to repository 'mavenLocal'
     &gt; Invalid publication 'mavenJava': multiple artifacts with the identical extension and classifier ('zip', 'null').
  </code></pre>
  <h3>Background:</h3>
  <p>Consider the following project structure:</p>
  <pre><code>.
  ├── aSrcFiles
  │   ├── a-1.txt
  │   └── a-2.txt
  ├── bSrcFiles
  │   ├── b-1.txt
  │   └── b-2.txt
  ├── build
  │   └── dist
  └── build.gradle.kts
  </code></pre>
  <p>And here is the following <code>build.gradle.kts</code> file:</p>
  <pre class="lang-kotlin prettyprint-override"><code>group = &quot;org.demo&quot;
  version = &quot;DEV-SNAPSHOT&quot;
  
  plugins { `maven-publish` }
  repositories(RepositoryHandler::mavenCentral)
  
  val assembleASrcFiles = tasks.register&lt;Zip&gt;(&quot;assembleASrcFiles&quot;) {
      archiveFileName.set(&quot;demo-${project.version}-aSrcFiles.zip&quot;)
      destinationDirectory.set(layout.buildDirectory.dir(&quot;dist&quot;))
      from(layout.projectDirectory.dir(&quot;aSrcFiles&quot;))
  }
  
  val assembleBSrcFiles = tasks.register&lt;Zip&gt;(&quot;assembleBSrcFiles&quot;) {
      archiveFileName.set(&quot;demo-${project.version}-bSrcFiles.zip&quot;)
      destinationDirectory.set(layout.buildDirectory.dir(&quot;dist&quot;))
      from(layout.projectDirectory.dir(&quot;bSrcFiles&quot;))
  }
  
  publishing {
      publications {
          create&lt;MavenPublication&gt;(&quot;mavenJava&quot;) {
              groupId = &quot;org.demo&quot;
              artifactId = &quot;demo&quot;
              artifact(assembleASrcFiles)
              artifact(assembleBSrcFiles)
          }
      }
  }
  </code></pre>
  <p>Running <code>maven-publish</code> task <code>publishToMavenLocal</code> with this setup fails to publish to repository 'mavenLocal'. This issue only happens when I introduce another artifact with the same extension (e.g. another ZIP file).</p>
  <p>Am I doing anything wrong? Regards.</p>