Bug 166315 Combo box doesn't allow blank when set string type in parameter editor
Combo box doesn't allow blank when set string type in parameter editor Steps to reproduce: 1.New a parameter, display type is Combo Box 2.Select data type as String Expected result: "Allow blank values" is enable. Actual result: "Allow blank values" is gray and can't be checked.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
for ( Iterator iter = choiceList.iterator( ); iter.hasNext( ); )
		{
			SelectionChoice choice = (SelectionChoice) iter.next( );
			if ( isValidValue( choice.getValue( ) ) != null
					|| containValue( choice, choice.getValue( ), COLUMN_VALUE ) )
			{
				iter.remove( );
			}
		}
	}
	private void changeControlType( )
	{
		if ( isStatic( ) )
		{
			String type = getSelectedControlType( );
			if ( !type.equals( lastControlType ) )
			{
				if ( DesignChoiceConstants.PARAM_CONTROL_CHECK_BOX.equals( type ) )
				{
					clearArea( valueArea );
					switchToCheckBox( );
				}
				else if ( PARAM_CONTROL_COMBO.equals( type )
						|| PARAM_CONTROL_LIST.equals( type )
						|| DesignChoiceConstants.PARAM_CONTROL_RADIO_BUTTON.equals( type ) )
				{
					
					if ( !PARAM_CONTROL_COMBO.equals( lastControlType )
							&& !PARAM_CONTROL_LIST.equals( lastControlType )
							&& !DesignChoiceConstants.PARAM_CONTROL_RADIO_BUTTON.equals( lastControlType ) )