I have a platform event trigger that takes in a json string which contains an array of objects. My postman test call looks like this:


(note that the quotes are each escaped with backslashes but when I submit this Stack Exchange post, it removes them)

My trigger uses json.deserializeUntyped like this:

List<Object> lstTestCodes = (List<Object>) JSON.deserializeUntyped(evt.testCodeList__c);

This trigger code works just fine, however I cannot get my test class to work. Inside the test class I am setting up a platform event with this parameter:

  testOrder.testCodeList__c = '[{"testCode":"000000","testName":"AAA","procedureClass":"XX"},{"testCode":"111111","testName":"BBB","procedureClass":"YY"},{"testCode":"222222","testName":"CCC","procedureClass":"ZZ"}]';

And when I run the test class, I get 'null input to JSON parser'. I have tried both escaping the quotes with backslash, and not escaping them, but I get the same problem. I have done a ton of Googling. Can anyone show me how I can set up my variable in my Apex test class? thanks!

  • Can you put log before this line and check JSON is properly populating there. Try to validate JSON on sites like jsonlint.com(I don't own the site, use at your discretion).
    – Ysr Shk
    Commented Apr 14, 2021 at 12:12
  • From the error, it feels that in the JSON.deserializeUntyped the value is getting null
    – Ysr Shk
    Commented Apr 14, 2021 at 12:13

1 Answer 1


I would make yourself a small inner class:

public class TestCode {
    public String testCode;
    public String testName;
    public String procedureClass;

Use it to both deserialize the incoming json:

TestCode[] codes = (TestCode[])JSON.deserialize(jsonString,TestCode[].class);

And generate the codes you need for your unit test :

new ParentClass.TestCode[] testCodeList = new ParentClass.TestCode[]{
testOrder.testCodeList__c = JSON.serialize(testCodeList);

I have parent class prefixed above because you'd likely be calling the second code block from the unit test class (I'm assuming)

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