Extending CpsScript Impossible?

CpsScriptMock.groovy

// Fails to compile with:
// CpsScriptMock.java:15: error: unreported exception IOException; must be caught or declared to be thrown
// But i'm throwing it right?
package demo.ci

import org.jenkinsci.plugins.workflow.cps.CpsScript

class CpsScriptMock extends CpsScript {
  CpsScriptMock()  throws IOException {
   }

  @Override
  Object run() {
    return null
  }

}