テンプレート処理中にエラーが発生しました。

The following has evaluated to null or missing:
==> channel.items  [in template "3192443#3192485#null" at line 8, column 30]

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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: #assign channelId = channel.items[0].id  [in template "3192443#3192485#null" at line 8, column 9]
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1<#if themeDisplay?has_content> 

2	<#assign scopeGroupId = themeDisplay.getScopeGroupId() /> 

3</#if> 

4 

5<#assign channel = restClient.get("/headless-commerce-delivery-catalog/v1.0/channels?accountId=-1&filter=name eq 'Marketplace Channel' and siteGroupId eq '${scopeGroupId}'") /> 

6 

7<#if channel?has_content> 

8	<#assign channelId = channel.items[0].id /> 

9</#if> 

10 

11<#if (CPDefinition_cProductId.getData())??> 

12	<#assign productId = CPDefinition_cProductId.getData() /> 

13</#if> 

14 

15<#assign 

16	product = restClient.get("/headless-commerce-delivery-catalog/v1.0/channels/"+ channelId +"/products/"+ productId +"?accountId=-1&images.accountId=-1&nestedFields=images") 

17	productImage = product.images?filter(item -> item.tags?seq_contains("app icon"))![] 

18/> 

19 

20<#if productImage?has_content> 

21	<#assign productThumbnail = productImage[0].src?split("/o") /> 

22	<#if productThumbnail?has_content && productThumbnail?size gte 2> 

23		<#assign productThumbnail1 = "/o/${productThumbnail[1]}"!"" /> 

24	<#else> 

25		<#assign productThumbnail1 = "/o/commerce-media/default/?groupId=${scopeGroupId}" /> 

26	</#if> 

27<#else> 

28	<#if product.urlImage?has_content> 

29		<#assign productThumbnail = product.urlImage?split("/o") /> 

30		<#if productThumbnail?has_content && productThumbnail?size gte 2> 

31			<#assign productThumbnail1 = "/o/${productThumbnail[1]}"!"" /> 

32		<#else> 

33			<#assign productThumbnail1 = "/o/commerce-media/default/?groupId=${scopeGroupId}" /> 

34		</#if> 

35	<#else> 

36		<#assign productThumbnail1 = "/o/commerce-media/default/?groupId=${scopeGroupId}" /> 

37	</#if> 

38</#if> 

39 

40${productThumbnail1}