Bug 67890 [PropertiesView] Exception when entries added to properties view
bundles/org.eclipse.ui.views/src/org/eclipse/ui/views/properties/PropertySheetViewer.java
cellEditor.activate();
        
        Control control = cellEditor.getControl();
        if (control == null) {
            cellEditor.deactivate();
            cellEditor = null;
            return;
        }
        
        cellEditor.addListener(editorListener);
        
        CellEditor.LayoutData layout = cellEditor.getLayoutData();
        treeEditor.horizontalAlignment = layout.horizontalAlignment;
        treeEditor.grabHorizontal = layout.grabHorizontal;
        treeEditor.minimumWidth = layout.minimumWidth;
        treeEditor.setEditor(control, item, columnToEdit);
        
        setErrorMessage(cellEditor.getErrorMessage());
        
        cellEditor.setFocus();
        
        fireCellEditorActivated(cellEditor);
    }
    /**
     * Adds a cell editor activation listener. Has no effect if an identical
     * activation listener is already registered.
     * 
     * @param listener
     *            a cell editor activation listener