FreeMarker template error (HTML_DEBUG mode; use RETHROW in production!)

The following has evaluated to null or missing:
==> Content  [in template "anesec_pc/template/solution.template.html" at line 27, column 55]

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Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
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FTL stack trace ("~" means nesting-related):
	- Failed at: ${Content.title}  [in template "anesec_pc/template/solution.template.html" at line 27, column 53]
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Java stack trace (for programmers):
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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.DollarVariable.calculateInterpolatedStringOrMarkup(DollarVariable.java:104)
	at freemarker.core.DollarVariable.accept(DollarVariable.java:63)
	at freemarker.core.Environment.visit(Environment.java:335)
	at freemarker.core.Environment.visit(Environment.java:341)
	at freemarker.core.Environment.process(Environment.java:314)
	at com.chestnut.common.staticize.StaticizeService.process(StaticizeService.java:78)
	at com.chestnut.contentcore.service.impl.PublishServiceImpl.doCatalogStaticize(PublishServiceImpl.java:419)
	at com.chestnut.contentcore.service.impl.PublishServiceImpl.catalogStaticize(PublishServiceImpl.java:370)
	at com.chestnut.contentcore.service.impl.PublishServiceImpl.catalogStaticize(PublishServiceImpl.java:360)
	at com.chestnut.contentcore.publish.CatalogPublishTask.publish(CatalogPublishTask.java:43)
	at com.chestnut.contentcore.publish.PublishTaskReceiver.onMessage(PublishTaskReceiver.java:42)
	at com.chestnut.contentcore.publish.PublishTaskReceiver.onMessage(PublishTaskReceiver.java:22)
	at org.springframework.data.redis.stream.StreamPollTask.deserializeAndEmitRecords(StreamPollTask.java:157)
	at org.springframework.data.redis.stream.StreamPollTask.doLoop(StreamPollTask.java:128)
	at org.springframework.data.redis.stream.StreamPollTask.run(StreamPollTask.java:112)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)