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
{
						String result = null;
						if ( DesignChoiceConstants.COLUMN_DATA_TYPE_DATETIME.equals( selectedParameter.getDataType( ) ) )
						{
							result = formatter.format( iter.getDate( columnBindingName ) );
						}
						else
						{
							result = iter.getString( columnBindingName );
						}
						if ( !StringUtil.isBlank( result )
								&& !valueList.contains( result ) )
						{
							valueList.add( result );
						}
					}
				}
				results.close( );
			}
		}
		catch ( Exception e )
		{
			ExceptionHandler.handle( e );
			return Collections.EMPTY_LIST;
		}
		return valueList;
	}
	private void createOptionsPart( Composite parent )
	{
		optionsGroup = new Group( parent, SWT.NULL );