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
selectedParameter.setMustMatch( false );
						}
						else if ( PARAM_CONTROL_LIST.equals( newControlType ) )
						{
							newControlType = DesignChoiceConstants.PARAM_CONTROL_LIST_BOX;
							
							selectedParameter.setMustMatch( true );
						}
						else
						{
							selectedParameter.setProperty( ScalarParameterHandle.MUCH_MATCH_PROP,
									null );
						}
						selectedParameter.setControlType( newControlType );
					}
					catch ( SemanticException e1 )
					{
						ExceptionHandler.handle( e1 );
					}
				}
			}
		} );
		createLabel( propertiesGroup, LABEL_DEFAULT_VALUE, maxStrLengthProperty );
		
		defaultValueChooser = new Combo( propertiesGroup, SWT.BORDER );
		defaultValueChooser.setLayoutData( new GridData( GridData.FILL_HORIZONTAL ) );
		defaultValueChooser.add( CHOICE_SELECT_VALUE );
		defaultValueChooser.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )