InvalidReferenceException when rendering an article template

Issue

• Adding a new field in an existing estructure produces an InvalidReferenceException in articles unless you update them if you try to render this field in a template:

  freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
  at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
  at freemarker.core.UnexpectedTypeException.newDescriptionBuilder(UnexpectedTypeException.java:85)
  at freemarker.core.UnexpectedTypeException.<init>(UnexpectedTypeException.java:48)
  at freemarker.core.NonHashException.<init>(NonHashException.java:49)
  at freemarker.core.Dot._eval(Dot.java:48)
  at freemarker.core.Expression.eval(Expression.java:101)
  at freemarker.core.MethodCall._eval(MethodCall.java:55)
  at freemarker.core.Expression.eval(Expression.java:101)
  at freemarker.core.Assignment.accept(Assignment.java:134)
  at freemarker.core.Environment.visit(Environment.java:331)
  at freemarker.core.Environment.visit(Environment.java:337)
  at freemarker.core.Environment.visit(Environment.java:337)
  at freemarker.core.Environment.process(Environment.java:310)
  at freemarker.template.Template.process(Template.java:383)
  at com.liferay.portal.template.freemarker.internal.FreeMarkerTemplate.processTemplate(FreeMarkerTemplate.java:154)
  at com.liferay.portal.template.BaseTemplate.processTemplate(BaseTemplate.java:163)
  at com.liferay.journal.internal.transformer.JournalTransformer.doTransform(JournalTransformer.java:367)
  at com.liferay.journal.internal.transformer.JournalTransformer.transform(JournalTransformer.java:103)

Environment

• Liferay DXP 7.0
• Liferay DXP 7.1
• Liferay DXP 7.2
• Liferay DXP 7.3
• Liferay DXP 7.4

Resolution

• The problem here is that the structure has a field but the article content does not, so if you try to render the structure the field will be null and it will throw a null pointer exception when the getData() method is used.
• This NPE will be shown as the InvalidReferenceException by the template engine.
• The solution is to add a null check in the template for this kind of fields to avoid rendering them if they are null.
• Instead of rendering it like

  <#assign field = field.getData()>

  you could use

  <#if field?? && field.getData()?? >
      <#assign field = field.getData()>
  <#else>
      <#assign field = "">
  </#if>