code: public static <T> Opt<T> fromCollection(Collection<T> col) {
          if (col.isEmpty()) {
              return absent();
          }
          if (col.size() == 1) {
              return of(col.iterator().next());
          }
          throw new IllegalArgumentException("Cannot create an Opt from a Collection with a size greater then 1!");
      }
docs: Create an {@code Opt} instance out of a {@code Collection}. The collection's size may not be greater than 1.
  Returns a non-empty {@code Opt} with the collection's only element if the collection is non-empty,
  or an empty {@code Opt} otherwise.
  
  @param col Collection to extract an {@code Opt} out of. The collection's size may not be greater than 1.
  @param <T> Collection type.
  @return A non-empty {@code Opt} if the {@code Collection} has a single element, or an empty one otherwise.
  @throws IllegalArgumentException If the collection's size is greater than 1.