@Override
    public void close() {
        consumed = true;

        if (closeHandlers == null || closeHandlers.isEmpty()) {
            return;
        }

        closeHandlers.forEach(Runnable::run);
        closeHandlers = null;
    }
Creates and returns an optimized sequential {@link Stream} implementation
with only a single element if the element is non-null. if the element is
null, an empty Stream is returned.

@param element the single element or null
@param <T> the type of the stream elements
@return a singleton sequential stream
common-parent/singletonstream/src/main/java/com/speedment/common/singletonstream/SingletonStream.java