Bug 153523 OK button in parameter dialog is enabled without default value in combo-box
Description: OK button in parameter dialog is enabled without default value in combo-box Steps to reproduce: 1. New a report parameter, combo-box. 2. Click New button, input abc as value, click OK 3. Set abc as default value and close Edit Parameter dialog. 4. New a data source and dataset 5. Edit the parameter, remove abc value and import values from dataset Expected result: OK button is disabled for there is no default value. Actual result: OK button is enabled.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
Integer.parseInt( listLimit.getText( ) );
						oldValue = listLimit.getText( );
					}
				}
				catch ( NumberFormatException e1 )
				{
					ExceptionHandler.openErrorMessageBox( ERROR_TITLE_INVALID_LIST_LIMIT,
							MessageFormat.format( ERROR_MSG_INVALID_LIST_LIMIT,
									new Object[]{
										Integer.toString( Integer.MAX_VALUE )
									} ) );
					listLimit.setText( oldValue );
				}
			}
		} );
		new Label( limitArea, SWT.NONE ).setText( LABEL_VALUES );
		allowNull = new Button( composite, SWT.CHECK );
		allowNull.setText( BUTTON_ALLOW_NULL_VALUE );
		allowNull.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		allowNull.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				if ( selectedParameter != null
						&& selectedParameter != newParameter )
				{
					try
					{
						selectedParameter.setAllowNull( allowNull.getSelection( ) );
					}
					catch ( SemanticException e1 )