Fatal error when using map tag in a blog entry to refer to config node

I create a blog entry, add the following HTML to the body:

<map>mapbuilder/config/16</map>

The following error is thrown:

Fatal error: Call to undefined function path_to_url() in /[...]sites/all/modules/mapbuilder/mapbuilder.module on line 821

At line 821 is the following function, which has been commented out:

function path_to_url( $path ) {
  $parts = parse_url( $path );
  //drupal_set_message( var_export($path,true) );
  if( isset($parts['scheme']) )
    return $path;
 
  if( $path[0] == '/' )
    return 'http://' . $_SERVER['HTTP_HOST'] . $path;
 
  global $base_url;
  return $base_url . '/' . $path;
}

When I uncomment the function, the page displays.