title: Missing Required Parameter in Docker File
body: <p>I'm learning how to use Jenkins and jenkinsfile for my CI/CD project, and when trying to run a docker image to run my selenium tests against, an error is thrown saying that the docker image param is missing. </p>
  
  <p>I've followed the docks on the jenkins site for a tutorial and I'm now trying to fit that for my own purposes. </p>
  
  <pre><code>pipeline {
  agent any
  
  stages {
      stage('Build') {
          steps {
              echo 'Building..'
              sh 'npm install'
          }
      }
      stage('Test') {
          steps {
              echo 'Testing..'
               docker {
                          image 'selenium/standalone-firefox:3.141.59-gold' 
                          args '-p 4444:4444' 
                  }
              sh 'npm test'
          }
      }
      stage('Deploy') {
          steps {
              echo 'Deploying....'
          }
      }
   }
  }
  </code></pre>
  
  <p>Docker should run on my Ubuntu server with port 4444 of the docker exposed and mapped to port 4444 of the server. </p>