def METHOD_NAME(self, context, *args):
    '''Verify that the thumbnail actually exists. If it does not then use the site image.
    Call example: 'mnvXpath:spitzerThumbnailLink('dummy')'
    return the thumbnail url
    '''
    if not self.persistence['spitzerThumbnailLink']:
        return ''
    else:
        return self.persistence['spitzerThumbnailLink']