reactfx/src/main/java/org/reactfx/ObservableBase.java
protected final void forEachObserver(Consumer<O> action) {
        ListHelper.forEach(observers, o -> action.accept(o));
    }
protected final void forEachObserver(Consumer<O> action) {
        ListHelper.forEach(observers, o -> action.accept(o));
    }
Executes action for each observer, regardless of recursion state.
If {@code action} throws an exception for one observer, it will not
be called for any subsequent observers and the exception will be
propagated by this method.
@param action action to execute for each observer.