Bug 164247 [DataBinding] NPE from ObservableMapLabelProvider when value is null
When a null value is to be returned from getColumnText(...) a NPE is thrown. It's trying to do a toString() on the null value.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/viewers/ObservableMapLabelProvider.java
*/
	public ObservableMapLabelProvider(IObservableMap[] attributeMaps) {
		this.attributeMaps = attributeMaps;
		for (int i = 0; i < attributeMaps.length; i++) {
			attributeMaps[i].addMapChangeListener(mapChangeListener);
		}
	}
	public void dispose() {
		for (int i = 0; i < attributeMaps.length; i++) {
			attributeMaps[i].removeMapChangeListener(mapChangeListener);
		}
		super.dispose();
	}
	public Image getImage(Object element) {
		return null;
	}
	public String getText(Object element) {
		return getColumnText(element, 0);
	}
	public Image getColumnImage(Object element, int columnIndex) {
		return null;
	}
	public String getColumnText(Object element, int columnIndex) {
		if (columnIndex < attributeMaps.length) {
			return attributeMaps[columnIndex].get(element).toString();
		}
		return null;
	}
}