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/ParameterDialog.java
} );
		Label values = new Label( limitArea, SWT.NULL );
		values.setText( Messages.getString( "ParameterDialog.Label.values" ) ); 
		values.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		
		createLabel( moreOptionSection, null ); 
		Composite checkBoxArea = new Composite( moreOptionSection, SWT.NONE );
		checkBoxArea.setLayout( UIUtil.createGridLayoutWithoutMargin( 2, false ) );
		checkBoxArea.setLayoutData( new GridData( GridData.FILL_BOTH ) );
		allowNull = new Button( checkBoxArea, SWT.CHECK );
		allowNull.setText( CHECKBOX_ALLOW_NULL );
		addCheckBoxListener( allowNull, CHECKBOX_ALLOW_NULL );
		allowBlank = new Button( checkBoxArea, SWT.CHECK );
		allowBlank.setText( CHECKBOX_ALLOW_BLANK );
		addCheckBoxListener( allowBlank, CHECKBOX_ALLOW_BLANK );
		doNotEcho = new Button( checkBoxArea, SWT.CHECK );
		doNotEcho.setText( CHECKBOX_DO_NOT_ECHO );
		addCheckBoxListener( doNotEcho, CHECKBOX_DO_NOT_ECHO );
		isHidden = new Button( checkBoxArea, SWT.CHECK );
		isHidden.setText( CHECKBOX_HIDDEN );
		addCheckBoxListener( isHidden, CHECKBOX_HIDDEN );
		needSort = new Button( checkBoxArea, SWT.CHECK );
		needSort.setText( CHECKBOX_SORT );
		addCheckBoxListener( needSort, CHECKBOX_SORT );
	}
	/**
	 * Set the input of the dialog, which cannot be null
	 * 
	 * @param input
	 *            the input of the dialog, which cannot be null