What I want to do is to select a certain value in a dropdownfield by default based on the value of the parent (that has the exact same dropdownfield). Why can't I get this field to display the parent value by default in the CMS?

public static $db = array(
  'ResponsibleOffice' => 'Int'
};

(...)

/**
  * Overload so that the default value is same as parent. 
  * Based on same function in BlogEntry.php
  */
  public function populateDefaults() {
    parent::populateDefaults();
      $this->setField('ResponsibleOffice', $parent->ResponsibleOffice);
  }

(...)

  public function getCMSFields() {
    $fields = parent::getCMSFields();

    $options = array('Value1', 'Value2', 'Value3', 'Value4');
    $fields->addFieldToTab("Root.Content.Main", new DropdownField("ResponsibleOffice", "Responsible office", $options), 'Content');

    return $fields;
  }	

Found populatedefaults recipe here. Following this example I now have:

	public function populateDefaults() {
		parent::populateDefaults();
		$parent_object = $this->getParent();
		$this->ResponsibleOffice = $parent_object->getField('ResponsibleOffice');
	}

Now, when adding this page as a child to another page, I get a 'Javascript parse error' in the CMS. What am I doing wrong?