Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
{
				if ( defaultValueChooser.getSelectionIndex( ) == -1 )
					return;
				String selection = defaultValueChooser.getItem( defaultValueChooser.getSelectionIndex( ) );
				if ( selection.equals( CHOICE_SELECT_VALUE ) )
				{
					defaultValueChooser.setText( "" );
					if ( getColumnValueList( ).isEmpty( ) )
						return;
					SelectParameterDefaultValueDialog dialog = new SelectParameterDefaultValueDialog( Display.getCurrent( )
							.getActiveShell( ),
							Messages.getString( "SelectParameterDefaultValueDialog.Title" ) );
					dialog.setColumnValueList( getColumnValueList( ) );
					int status = dialog.open( );
					if ( status == Window.OK )
					{
						String selectedValue = dialog.getSelectedValue( );
						if ( selectedValue != null )
							defaultValueChooser.setText( selectedValue );
					}
					else if ( status == Window.CANCEL )
					{
						defaultValueChooser.setText( "" );
					}
				}
				
			}
		} );
	}