formatter still broken

If formatter does not contain underscore than the $parts array will be empty since it is popped at the second line, so the implode function will try to implode an empty array

$parts =  explode('_', $formatter);
$style = array_pop($parts);
$presetname = implode('_', $parts);

Solution

  // Check if there is an underscore in the formatter name
  if (strpos($formatter, '_')) {
    preg_match('/^(.*)_(linked|imagelink|path|url)?$/', $formatter, $matches);
    // Shift the first element of regex match since it contains the whole string (formatter)
    array_shift($matches);
    list($presetname, $style) = $matches;
  }
  else {
    $presetname = $formatter;
  }