default EditableValueHolderState getFilterValueHolder(FacesContext context) {
        UIComponent filterFacet = getFacet("filter");
        if (filterFacet != null) {
            AtomicReference<EditableValueHolderState> stateRef = new AtomicReference<>(null);
            CompositeUtils.invokeOnDeepestEditableValueHolder(context, filterFacet, (fc, target) -> {
                EditableValueHolderState state = new EditableValueHolderState();
                state.setValue(((EditableValueHolder) target).getValue());
                stateRef.set(state);
            });
            return stateRef.get();
        }

        return null;
    }
Special {@link #getColumnKey()} method which must be used when we are inside e.g.
the DataTable "row state".

@param parent
@param rowKey
@return
primefaces/src/main/java/org/primefaces/component/api/UIColumn.java