code: public static boolean[] toArray(Collection<Boolean> collection) {
      if (collection instanceof BooleanArrayAsList) {
        return ((BooleanArrayAsList) collection).toBooleanArray();
      }
  
      Object[] boxedArray = collection.toArray();
      int len = boxedArray.length;
      boolean[] array = new boolean[len];
      for (int i = 0; i < len; i++) {
        // checkNotNull for GWT (do not optimize)
        array[i] = (Boolean) checkNotNull(boxedArray[i]);
      }
      return array;
    }
docs: Copies a collection of {@code Boolean} instances into a new array of primitive {@code boolean}
  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.
  
  <p><b>Note:</b> consider representing the collection as a {@link java.util.BitSet} instead.
  
  @param collection a collection of {@code Boolean} 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