agent {
      dockerfile true
}

agent {
   node {
      label 'has-docker'
      dockerfile true
   }
}

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 2: Only one agent type is allowed per agent section @ line 2, column 5.
       agent {
       ^

WorkflowScript: 2: No agent type specified. Must be one of [docker, dockerfile, label, any, none] @ line 2, column 5.
       agent {