philwebb/DemoApplication.java

## DemoApplication.java
package com.example.demo;

import java.util.Collection;

import org.springframework.beans.factory.ObjectProvider;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.thymeleaf.context.IExpressionContext;
import org.thymeleaf.dialect.IDialect;
import org.thymeleaf.spring5.SpringTemplateEngine;
import org.thymeleaf.spring5.dialect.SpringStandardDialect;
import org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator;
import org.thymeleaf.standard.expression.IStandardVariableExpression;
import org.thymeleaf.standard.expression.IStandardVariableExpressionEvaluator;
import org.thymeleaf.standard.expression.StandardExpressionExecutionContext;
import org.thymeleaf.templateresolver.ITemplateResolver;

@SpringBootApplication
public class DemoApplication {

	@Bean
	public SpringTemplateEngine templateEngine(
			Collection<ITemplateResolver> templateResolvers,
			ObjectProvider<IDialect> dialects) {
		SpringTemplateEngine engine = new SpringTemplateEngine();
		templateResolvers.forEach(engine::addTemplateResolver);
		dialects.orderedStream().forEach(engine::addDialect);
		engine.setDialect(new ExtendedSpringDialect());
		return engine;
	}

	public static void main(String[] args) {
		SpringApplication.run(DemoApplication.class, args);
	}

	private static class ExtendedSpringDialect extends SpringStandardDialect {

		@Override
		public IStandardVariableExpressionEvaluator getVariableExpressionEvaluator() {
			return NullSafeSPELVariableExpressionEvaluator.INSTANCE;
		}

	}

	private static class NullSafeSPELVariableExpressionEvaluator implements
			IStandardVariableExpressionEvaluator {

		private static final NullSafeSPELVariableExpressionEvaluator INSTANCE = new NullSafeSPELVariableExpressionEvaluator();

		@Override
		public Object evaluate(IExpressionContext context,
				IStandardVariableExpression expression,
				StandardExpressionExecutionContext expContext) {
			return postProcess(SPELVariableExpressionEvaluator.INSTANCE.evaluate(context,
					expression, expContext));
		}

		private Object postProcess(Object result) {
			if (result == null) {
				return "- -";
			}
			return result;
		}

	}

}

## hello.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Getting Started: Serving Web Content</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
    <p th:text="'Hello, ' + ${{first}} + ' ' + ${{last}} + '!'" />
</body>
</html>

## MyController.java
package com.example.demo;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class MyController {

	@RequestMapping("/hello")
	public ModelAndView hello() {
		ModelAndView modelAndView = new ModelAndView("hello");
		modelAndView.addObject("first", "Phil");
		modelAndView.addObject("last", null);
		return modelAndView;
	}

}
	package com.example.demo;

	import java.util.Collection;

	import org.springframework.beans.factory.ObjectProvider;
	import org.springframework.boot.SpringApplication;
	import org.springframework.boot.autoconfigure.SpringBootApplication;
	import org.springframework.context.annotation.Bean;
	import org.thymeleaf.context.IExpressionContext;
	import org.thymeleaf.dialect.IDialect;
	import org.thymeleaf.spring5.SpringTemplateEngine;
	import org.thymeleaf.spring5.dialect.SpringStandardDialect;
	import org.thymeleaf.spring5.expression.SPELVariableExpressionEvaluator;
	import org.thymeleaf.standard.expression.IStandardVariableExpression;
	import org.thymeleaf.standard.expression.IStandardVariableExpressionEvaluator;
	import org.thymeleaf.standard.expression.StandardExpressionExecutionContext;
	import org.thymeleaf.templateresolver.ITemplateResolver;

	@SpringBootApplication
	public class DemoApplication {

	@Bean
	public SpringTemplateEngine templateEngine(
	Collection<ITemplateResolver> templateResolvers,
	ObjectProvider<IDialect> dialects) {
	SpringTemplateEngine engine = new SpringTemplateEngine();
	templateResolvers.forEach(engine::addTemplateResolver);
	dialects.orderedStream().forEach(engine::addDialect);
	engine.setDialect(new ExtendedSpringDialect());
	return engine;
	}

	public static void main(String[] args) {
	SpringApplication.run(DemoApplication.class, args);
	}

	private static class ExtendedSpringDialect extends SpringStandardDialect {

	@Override
	public IStandardVariableExpressionEvaluator getVariableExpressionEvaluator() {
	return NullSafeSPELVariableExpressionEvaluator.INSTANCE;
	}

	}

	private static class NullSafeSPELVariableExpressionEvaluator implements
	IStandardVariableExpressionEvaluator {

	private static final NullSafeSPELVariableExpressionEvaluator INSTANCE = new NullSafeSPELVariableExpressionEvaluator();

	@Override
	public Object evaluate(IExpressionContext context,
	IStandardVariableExpression expression,
	StandardExpressionExecutionContext expContext) {
	return postProcess(SPELVariableExpressionEvaluator.INSTANCE.evaluate(context,
	expression, expContext));
	}

	private Object postProcess(Object result) {
	if (result == null) {
	return "- -";
	}
	return result;
	}

	}

	}
	<!DOCTYPE HTML>
	<html xmlns:th="http://www.thymeleaf.org">
	<head>
	<title>Getting Started: Serving Web Content</title>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	</head>
	<body>
	<p th:text="'Hello, ' + ${{first}} + ' ' + ${{last}} + '!'" />
	</body>
	</html>
	package com.example.demo;

	import org.springframework.stereotype.Controller;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.servlet.ModelAndView;

	@Controller
	public class MyController {

	@RequestMapping("/hello")
	public ModelAndView hello() {
	ModelAndView modelAndView = new ModelAndView("hello");
	modelAndView.addObject("first", "Phil");
	modelAndView.addObject("last", null);
	return modelAndView;
	}

	}