Error handling variables in external tasks


i’m new to camunda and need help to get my small external task test process running. It should simply set a bool variable, but i always get the error
“{“type”:“NullValueException”,“message”:“condition expression returns null: result is null”}”
when i try to complete the task. This is independent from my .net core external task handling and also occurs when i use postman. So it maybe is a problem of the process definition itself?!?
Im using the version 4.4.0 of the modeler and bpm version 7.14.
Here comes the post body of the complete call:
“variables”: {
“ETOK”: {
“value”: true
“workerId”: “1”

The process definition is attached.
ETTest_v7.bpmn (5.9 KB)
Kind regards, J.Lucia

Hey @lucia,

I tried the process you posted with the payload you described, works all fine on my machine to be honest with 7.14.0 using Camunda Run.

Are you sure you are using the model version you posted? It sounds like the condition expressions on the sequence flows following the external task cannot be evaluated correctly.


Hi Tobias,

thank you for your helpful remark - it was an error of calling the wrong version of the process definiton!
I was fetching the Tasks with the “MaxTasks” setting set to 1 and was getting an old Task Instance.
Additionally i forgot to check the business-key.
Now, using the most recent process version, it works.
Remark: To get the right result, I also needed to remove the definition of the “ETOK” variable in the Output definition of the External Task thus the variable was always false after the complete call. I first thought the pre-definition of the variable was necessary - but it is not.

Greetings, J.Lucia

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