new DefaultComboBoxModel(ExpressionUtil.getInstance().getKnownExpressions());
model.insertElementAt(null, 0);
expressionEditor = new JComboBox(model);
expressionEditor.setEditable(true);
expressionEditor.setRenderer(new ExpressionListCellRenderer());
expressionEditor.setEditor(new ExpressionComboBoxEditor(true));
expressionEditor.getInputMap().put(UtilMessages.getInstance().getOptionalKeyStroke
("AbstractStringValueCellEditor.Popup.Accelerator"), POPUP_EDITOR);
expressionEditor.getActionMap().put(POPUP_EDITOR, new ExtendedEditorAction());
setLayout(new BorderLayout());