Bug 190727 [regression]Default value issue when switch report parameter from textbox to listbox.[0705]
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
if ( getSelectedDataType( ).equals( DesignChoiceConstants.PARAM_TYPE_STRING ) )
			{
				clearDefaultValueChooser( checkBox.getSelection( ) );
			}
			updateMessageLine( );
		}
	}
	private void clearDefaultValueChooser( boolean isChecked )
	{
		if ( isChecked )
		{
			clearDefaultValueText( );
			clearDefaultValueChooserSelections( );
		}
		else
		{
			if ( defaultValueChooser == null
					|| defaultValueChooser.isDisposed( )
					|| defaultValueChooser.getItemCount( ) > 1 )
				return;
			defaultValueChooser.add( CHOICE_NULL_VALUE );
			defaultValueChooser.add( CHOICE_BLANK_VALUE );
		}
	}
	private void clearArea( Composite area )
	{
		Control[] children = area.getChildren( );
		for ( int i = 0; i < children.length; i++ )
		{
			children[i].dispose( );