Bug 294738 [Viewers] (JFace) Assertion for missing LabelProvider in ViewerColumn
ViewerColumn should throw an AssertionException if the LabelProvider is missing for a column to provide a helpful error message.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerColumn.java
private CellLabelProvider labelProvider;
	static String COLUMN_VIEWER_KEY = Policy.JFACE + ".columnViewer";
	private EditingSupport editingSupport;
	private ILabelProviderListener listener;
	private boolean listenerRegistered = false;
	private ColumnViewer viewer;
	/**
	 * Create a new instance of the receiver at columnIndex.
	 * 
	 * @param viewer
	 *            the viewer the column is part of
	 * @param columnOwner