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/ParameterDialog.java
inputParameter.setLabelExpr( getExpression( displayTextChooser.getText( ) ) );
				}
				if ( dirtyProperties.containsKey( CHECKBOX_DISTINCT ) )
				{
					inputParameter.setDistinct( !getProperty( CHECKBOX_DISTINCT ) );
				}
				if ( sortKeyChooser.getText( ).equals( CHOICE_DISPLAY_TEXT ) )
				{
					inputParameter.setSortBy( DesignChoiceConstants.PARAM_SORT_VALUES_LABEL );
				}
				else if ( sortKeyChooser.getText( )
						.equals( CHOICE_VALUE_COLUMN ) )
				{
					inputParameter.setSortBy( DesignChoiceConstants.PARAM_SORT_VALUES_VALUE );
				}
				if ( sortDirectionChooser.getText( ).equals( NONE_DISPLAY_TEXT ) )
				{
					inputParameter.setSortDirection( null );
				}
				else if ( sortKeyChooser.getText( ).equals( CHOICE_ASCENDING ) )
				{
					inputParameter.setSortDirection( DesignChoiceConstants.SORT_DIRECTION_ASC );
				}
				else
				{
					inputParameter.setSortDirection( DesignChoiceConstants.SORT_DIRECTION_DESC );
				}
			}
			
			inputParameter.setHelpText( UIUtil.convertToModelString( helpTextEditor.getText( ),