public LazyImmutable<T> setOnce(final T val) {
        this.value.compareAndSet(UNSET, val);
        set.set(true);
        return this;

    }
public LazyImmutable < T > setOnce ( final T val ) { this . value . compareAndSet ( UNSET , val ) ; set . set ( true ) ; return this ; }
Set the value of this ImmutableClosedValue
If it has already been set will throw an exception

@param val Value to set to
@return Current set Value