title: Jenkinsfile get current tag
body: <p>Is there a way to get the current tag ( or null if there is none ) for a job in a Jenkinsfile? The background is that I only want to build some artifacts ( android APKs ) when this commit has a tag. 
  I tried:</p>
  
  <pre><code>env.TAG_NAME
  </code></pre>
  
  <p>and</p>
  
  <pre><code>binding.variables.get("TAG_NAME")
  </code></pre>
  
  <p>both are always null - even though this ( <a href="https://issues.jenkins-ci.org/browse/JENKINS-34520" rel="noreferrer">https://issues.jenkins-ci.org/browse/JENKINS-34520</a> ) indicates otherwise </p>