Calling get() on an Optional that is not present will result in a NoSuchElementException.

This check detects cases where get() is called when the optional is definitely not present, e.g.:

if (!o.isPresent()) {
  return o.get(); // this will throw a NoSuchElementException
}

if (o.isEmpty()) {
  return o.get(); // this will throw a NoSuchElementException
}

These cases are almost definitely bugs; the intent may have been to invert the test:

if (o.isPresent()) {
  return o.get();
}