Topdesk/FreeMarker流程开发：获取访客预期到达日期时出现空值评估错误求助

Let's break down the possible causes and fixes for the null evaluation error you're seeing, even though your first step confirms the response stored successfully:

1. Mismatched Field Name (Most Likely Culprit) #

Looking at your error log, it complains about _responses.GetVisitorData.body.verwachteaankomst being null—but in your validation expression, you referenced ${_responses.GetVisitorData.body.expectedArival}.

verwachteaankomst is Dutch for "expected arrival"—this means the Topdesk API returns the field under its native Dutch name, not the English expectedArival you assumed.

Fix: Update your expression to use the correct field name from the error:

${_responses.GetVisitorData.body.verwachteaankomst?string["dd MMMM yyyy"] == now?string["dd MMMM yyyy"]}

(I added ?string here to safely format the date only if the field exists—we’ll cover null handling next.)

2. Verify the Exact API Response Structure #

Even with the right field name, the value might be nested deeper in the response body (e.g., under a visitor object or similar). The "stored successfully" message only confirms the response was saved, not that the field exists at the path you’re using.

Fix: Add a debug step to log the full response body so you can inspect its structure. Insert a step that outputs:

${_responses.GetVisitorData.body?string}

Check the logs to see where verwachteaankomst lives in the JSON hierarchy, then adjust your path accordingly (e.g., _responses.GetVisitorData.body.visitor.verwachteaankomst).

3. Handle Cases Where the Field Might Be Null #

Some visitor records might not have an expected arrival date set at all, making the field null even if the API returns a valid response.

Fix: Use FreeMarker’s null-safe operator ?? to check for the field’s existence before comparing, and handle missing values explicitly:

<#if _responses.GetVisitorData.body.verwachteaankomst??>
  ${_responses.GetVisitorData.body.verwachteaankomst?string["dd MMMM yyyy"] == now?string["dd MMMM yyyy"]}
<#else>
  <!-- Handle missing date (e.g., return false, log a warning) -->
  false
</#if>

4. Confirm Date Formatting Locale (Post-Null Fix) #

Once you resolve the null issue, watch out for locale mismatches: now?string["dd MMMM yyyy"] uses your Topdesk environment’s default locale. If the API returns dates with month names in a different language (like Dutch), the comparison might fail even if the dates are identical.

Fix: Explicitly set the locale for date formatting to match the API’s output. For Dutch locale:

${_responses.GetVisitorData.body.verwachteaankomst?string("dd MMMM yyyy", "nl_NL") == now?string("dd MMMM yyyy", "nl_NL")}

内容的提问来源于stack exchange，提问作者Max82