code: public static char[] toArray(Collection<Character> collection) {
      if (collection instanceof CharArrayAsList) {
        return ((CharArrayAsList) collection).toCharArray();
      }
  
      Object[] boxedArray = collection.toArray();
      int len = boxedArray.length;
      char[] array = new char[len];
      for (int i = 0; i < len; i++) {
        // checkNotNull for GWT (do not optimize)
        array[i] = (Character) checkNotNull(boxedArray[i]);
      }
      return array;
    }
docs: Copies a collection of {@code Character} instances into a new array of primitive {@code char}
  values.
  
  <p>Elements are copied from the argument collection as if by {@code collection.toArray()}.
  Calling this method is as thread-safe as calling that method.
  
  @param collection a collection of {@code Character} objects
  @return an array containing the same values as {@code collection}, in the same order, converted
  to primitives
  @throws NullPointerException if {@code collection} or any of its elements is null