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
choices[choices.length - 2] = DISPLAY_NAME_CONTROL_LIST;
				choices[choices.length - 1] = CONTROL_TYPE_CHOICE_SET.findChoice( DesignChoiceConstants.PARAM_CONTROL_RADIO_BUTTON )
						.getDisplayName( );
			}
			else
			{
				choices[0] = DISPLAY_NAME_CONTROL_COMBO;
				choices[1] = DISPLAY_NAME_CONTROL_LIST;
			}
			controlTypeChooser.setItems( choices );
			if ( originalSelection.length( ) == 0 )
			{
				controlTypeChooser.setText( getInputControlDisplayName( ) );
			}
			else
			{
				int index = controlTypeChooser.indexOf( originalSelection );
				if ( index == -1 )
				{
					
					controlTypeChooser.select( 0 );
					return true;
				}
				controlTypeChooser.setText( originalSelection );
			}
		}
		return false;
	}
	private void makeUniqueAndValid( )
	{