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
EditingSupport getEditingSupport() {
		return editingSupport;
	}
	/**
	 * Set the editing support. Subclasses may extend but must call the super
	 * implementation.
	 * <p>
	 * Users setting up an editable {@link TreeViewer} or {@link TableViewer} with more than 1 column <b>have</b>
	 * to pass the SWT.FULL_SELECTION style bit when creating the viewer
	 * </p>
	 * @param editingSupport
	 *            The {@link EditingSupport} to set.
	 */
	public void setEditingSupport(EditingSupport editingSupport) {
		this.editingSupport = editingSupport;
	}
	/**
	 * Refresh the cell for the given columnIndex. <strong>NOTE:</strong>the
	 * {@link ViewerCell} provided to this method is no longer valid after this
	 * method returns. Do not cache the cell for future use.
	 * 
	 * @param cell
	 *            {@link ViewerCell}
	 */
	void refresh(ViewerCell cell) {
		getLabelProvider().update(cell);
	}
	/**
	 * Disposes of the label provider (if set), unregisters the listener and
	 * nulls the references to the label provider and editing support. This