Thymleaf - Unsupported entity requested with PUBLICID "null"

Question

When using Thymleaf with Spring MVC I ran into this issue which just prints this stack trace.

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is
org.thymeleaf.exceptions.TemplateProcessingException: Unsupported entity requested with PUBLICID "null" and SYSTEMID "http://www.thymeleaf.org/dtd/xhtml1-strict-thymeleaf-4.dtd". Make sure a corresponding org.thymeleaf.doctype.resolution.IDocTypeResolutionEntry implementation is provided by you dialect
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727) 
root cause
org.thymeleaf.exceptions.TemplateProcessingException: Unsupported entity requested with PUBLICID "null" and SYSTEMID "http://www.thymeleaf.org/dtd/xhtml1-strict-thymeleaf-4.dtd". Make sure a corresponding org.thymeleaf.doctype.resolution.IDocTypeResolutionEntry implementation is provided by you dialect
org.thymeleaf.templateparser.EntityResolver.resolveEntity(EntityResolver.java:72)
org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser$XmlSAXHandler.resolveEntity(AbstractNonValidatingSAXTemplateParser.java:708)
org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser$XmlSAXHandler.resolveEntity(AbstractNonValidatingSAXTemplateParser.java:716)
com.sun.org.apache.xerces.internal.util.EntityResolver2Wrapper.resolveEntity(EntityResolver2Wrapper.java:173)
com.sun.org.apache.xerces.internal.impl.XMLEntityManager.resolveEntityAsPerStax(XMLEntityManager.java:1018)
com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.dispatch(XMLDocumentScannerImpl.java:1190)
com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$DTDDriver.next(XMLDocumentScannerImpl.java:1088)
com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:1001)
com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:647)
com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:513)
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:815)
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:744)
com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:128)
com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1208)
com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:543)
javax.xml.parsers.SAXParser.parse(SAXParser.java:395)
org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser.doParse(AbstractNonValidatingSAXTemplateParser.java:209)
org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser.parseTemplateUsingPool(AbstractNonValidatingSAXTemplateParser.java:133)
org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser.parseTemplate(AbstractNonValidatingSAXTemplateParser.java:116)
org.thymeleaf.TemplateRepository.getTemplate(TemplateRepository.java:277)
org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1104)
org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1060)
org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1011)
org.thymeleaf.spring4.view.ThymeleafView.renderFragment(ThymeleafView.java:335)
org.thymeleaf.spring4.view.ThymeleafView.render(ThymeleafView.java:190)
org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)

I am documenting this as a reference for future users who come across this issue, as this is not documented even in in the thymleaf site.

Answer 1

The problem was that I was using the wrong declaration in the DOCTYPE, since I was using spring mvc I should have used

For Spring 4

<!DOCTYPE html SYSTEM "http://www.thymeleaf.org/dtd/xhtml1-strict-thymeleaf-spring4-4.dtd">

For Spring 3

<!DOCTYPE html SYSTEM "http://www.thymeleaf.org/dtd/xhtml1-strict-thymeleaf-spring3-3.dtd">

Answer 2

Setting so helped me in spring boot, Spring version 4:

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:th="http://www.thymeleaf.org">