ComboBox removeAllItems() sets value to null

Hi.

We have two comboboxes A and B. B depends on A's value.

ComboBox A = new ComboBox();
A.setImmediate(true);

ComboBox B = new ComboBox();
B.setImmediate(true);

A.addValueChangeListener(event -> {
     Collection<Stirng> data = getData((String) event.getProperty().getValue());
     B.removeAllItems();
     B.addItems(data);
     B.setValue(B.getItemIds().iterator().next()); // i don't like such selection of the first item
});

initialLoad(A);

So far so good. 

We add some functionality that will replace all items in combobox A. 

repopulate(final Collection<String> newOptions) {
     if (newOptions.isEmpty()) {
          A.setEnabled(false);
          B.setEnabled(false);
     } else {
          A.setEnabled(true);
          B.setEnabled(true);
          A.removeAllItems();
          A.addItems(newOptions);
          A.setValue(A.getItemIds().iterator().next()); // again (
     }
}

So, pretty claer here, we clear items and add the new one. Reset value is needed to update the B combobox, but...!
RemoveAllItems also set the value, NULL value. And what we get in result? Replace items triggers two value change events: one is for NULL, second is for the first value. Which will be first? Who knows! One time it's NULL another is a real value. On UI it looks like empty combobox - but there is actually no reason for this from the user pov, then it looks good, then again empty and so on.

I have two options for this:
1) save listener to the field and remove/add it before removing all items and adding the new one;
2) recreate whole combobox (what?) with all realted stuff.

Actually, I don't like any of them.

Could it be implemented in some other way? Maybe I missed smth (high chance). Thanks in advance.