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

The following has evaluated to null or missing:
==> content.isBuy  [in template "netSecurity_h5/template/article_list.template.html" at line 182, column 62]

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Tip: It's the step after the last dot that caused this error, not those before it.
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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: #if content.isBuy == "1"  [in template "netSecurity_h5/template/article_list.template.html" at line 182, column 57]
	- Reached through: @cms_content catalogid="${Catalog.cat...  [in template "netSecurity_h5/template/article_list.template.html" at line 131, column 25]
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Java stack trace (for programmers):
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freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]
	at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
	at freemarker.core.EvalUtil.compare(EvalUtil.java:198)
	at freemarker.core.EvalUtil.compare(EvalUtil.java:115)
	at freemarker.core.ComparisonExpression.evalToBoolean(ComparisonExpression.java:78)
	at freemarker.core.ConditionalBlock.accept(ConditionalBlock.java:48)
	at freemarker.core.Environment.visit(Environment.java:335)
	at freemarker.core.Environment.visit(Environment.java:377)
	at freemarker.core.IteratorBlock$IterationContext.executedNestedContentForCollOrSeqListing(IteratorBlock.java:321)
	at freemarker.core.IteratorBlock$IterationContext.executeNestedContent(IteratorBlock.java:271)
	at freemarker.core.IteratorBlock$IterationContext.accept(IteratorBlock.java:244)
	at freemarker.core.Environment.visitIteratorBlock(Environment.java:645)
	at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:108)
	at freemarker.core.IteratorBlock.accept(IteratorBlock.java:94)
	at freemarker.core.Environment.visit(Environment.java:371)
	at freemarker.core.Environment$NestedElementTemplateDirectiveBody.render(Environment.java:3423)
	at com.chestnut.common.staticize.tag.AbstractTag.onTagEnd(AbstractTag.java:93)
	at com.chestnut.common.staticize.tag.AbstractTag.execute(AbstractTag.java:62)
	at freemarker.core.Environment.visit(Environment.java:452)
	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:102)
	at freemarker.core.Environment.visit(Environment.java:335)
	at freemarker.core.Environment.visit(Environment.java:341)
	at freemarker.core.Environment.process(Environment.java:314)
	at com.chestnut.common.staticize.StaticizeService.process(StaticizeService.java:99)
	at com.chestnut.contentcore.publish.staticize.CatalogStaticizeType.doCatalogStaticize(CatalogStaticizeType.java:174)
	at com.chestnut.contentcore.publish.staticize.CatalogStaticizeType.catalogStaticize(CatalogStaticizeType.java:100)
	at com.chestnut.contentcore.publish.staticize.CatalogStaticizeType.catalogStaticize(CatalogStaticizeType.java:91)
	at com.chestnut.contentcore.publish.staticize.CatalogStaticizeType.staticize(CatalogStaticizeType.java:83)
	at com.chestnut.contentcore.publish.strategies.ThreadPoolPublishStrategy.lambda$publish$0(ThreadPoolPublishStrategy.java:59)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:840)