Declaration of CustomSiteConfig::updateCMSFields() should be compatible with that of DataExtension::updateCMSFields()

class CustomSiteConfig extends DataExtension {

static $db = array(
   //Business Info
'BusinessName' => 'Varchar',
'StreetAddress' => 'Varchar',
'City' => 'Varchar',
'Province' => 'Varchar',
'PostalCode' => 'Varchar',
'PhoneNumber' => 'Varchar',
'FaxNumber' => 'Varchar',
'MainEmail' => 'Varchar',
'SiteEmail' => 'Varchar',
//Social Media
'Twitter' => 'Varchar',
'FacebookURL' => 'Varchar',
'GooglePlusURL' => 'Varchar',
'PinterestURL' => 'Varchar',
'YouTubeURL' => 'Varchar',
//About Info
'About' => 'HTMLText'
);

static $has_one = array(
   'Picture' => 'Image'
);

public function updateFormFields(FieldList &$fields) {
$fields->addFieldToTab("Root.Main", new TextField("BusinessName"));
$fields->addFieldToTab("Root.Main", new TextField("StreetAddress"));
$fields->addFieldToTab("Root.Main", new TextField("City"));
$fields->addFieldToTab("Root.Main", new TextField("Province"));
$fields->addFieldToTab("Root.Main", new TextField("PostalCode"));
$fields->addFieldToTab("Root.Main", new TextField("PhoneNumber"));
$fields->addFieldToTab("Root.Main", new TextField("FaxNumber"));
$fields->addFieldToTab("Root.Main", new EmailField("MainEmail", 'Main Contact Email'));
$fields->addFieldToTab("Root.Main", new EmailField("SiteEmail", 'Email for Contact Forms'));
$fields->addFieldToTab("Root.Main", new UploadField("Picture"));
$fields->addFieldToTab("Root.Main", new HtmlEditorField("About", "Sidebar About Copy"));
$fields->removeByName('Tagline');
$fields->addFieldToTab("Root.SocialMedia", new TextField("Twitter", 'Twitter User Name'));
$fields->addFieldToTab("Root.SocialMedia", new TextField("FacebookURL", 'Facebook URL'));
$fields->addFieldToTab("Root.SocialMedia", new TextField("GooglePlusURL", 'Google+ URL'));
$fields->addFieldToTab("Root.SocialMedia", new TextField("PinterestURL", 'Pinterest URL'));
$fields->addFieldToTab("Root.SocialMedia", new TextField("YouTubeURL", 'YouTube URL'));

}
}