Hi -
Be gentle - question is probably very newbie…
I have a use-case where I’d like to create a variable to input to a Service Task. I’ve read through the Feel documentation particularly around expressions but the editor doesn’t allow spaces?
I was thinking something like (lazy-load):
=if (new-variable = null) then new-variable = 1 else new-variable = new-variable + 1
is something like this possible?
Thanks.
Zeebie 0.23.1
Essi
Hi Essi,
welcome to the Zeebe community 
I’ve read through the Feel documentation particularly around expressions but the editor doesn’t allow spaces?
Good point. The zeebe-modeler plan to improve the UX for expressions. However, feel free to create an issue here: Issues · zeebe-io/zeebe-modeler · GitHub.
Yes. That should be possible in general. You could have an input mapping with a source expression
=if (new_variable = null) then 1 else new_variable + 1
and target new_variable.
Note that the variable name should not include an operator like -. Instead, it is recommended to use snake_case or camelCase.
Also, you need to ensure that the variable is present (i.e. initialized with null) before. Otherwise, we could lead to an unexpected behavior (A missing variable/nested property can not be handled · Issue #4212 · camunda/zeebe · GitHub).
Does this help you?
Do you want to discuss more about the context where the variable is used?
Best regards,
Philipp
Thank you - great reply. I also have an issue when doing arithmetic on durations. It always seems to return null?
e.g. =duration(process.GetCustomerAccounts.wait)+duration(process.GetCustomerAccounts.wait)
process.GetCustomerAccounts.wait has a value of “P0DT0H0M1S”
The expression looks good 
I assume that you create a variable with the name “process.GetCustomerAccounts.wait”, correct?
Again, a variable name should not include operators and . is also an operator 
Either rename the name or use a JSON object/document variable (e.g. {"GetCustomerAccounts":{"wait":"P0DT0H0M1S"}}).
Does this help you?
Hi Philipp - the variable is a context so its just navigation so I don’t think the variable name is the problem (I’m using variable names like this elsewhere without problems) - the Json looks like below:
{
“customerid”: “12345678”,
“GetCustomerAccounts” :
{
“executions” : 0,
“wait” : “P0DT0H0M1S”,
“maxRetries” : 3
}
}
If I just use the variable it all works and gets a delay of 1 second. If I use the expression below it returns NULL:
=duration(process.GetCustomerAccounts.wait)+duration(process.GetCustomerAccounts.wait)
Note: the variable name at the top I wasn’t using in the workflow - just a quick (bad) example.
It works for me. Let’s find out what is different 
Is this the value of the variable “process”?
Please share your BPMN and the commands/steps to reproduce the behavior.
The following command works for my example:
./bin/zbctl create instance Process_0e4u1od --variables="{\"customerid\": \"12345678\",\"GetCustomerAccounts\" :{\"executions\" : 0,\"wait\" : \"P0DT0H0M1S\",\"maxRetries\" : 3} }" --insecure
{
"workflowKey": 2251799813685298,
"bpmnProcessId": "Process_0e4u1od",
"version": 2,
"workflowInstanceKey": 2251799813685300
}
Hi philipp - getting error “Sorry, new users can only put 2 links in a post” - I’m assuming this relates to the http: links in the BPMN XML…
Thank you for sharing. That helped!
The difference is that you’re using the expression in the source expression of a variable output mapping. Currently, a temporal value can’t be stored directly as a variable. But it can be transferred into a string using the string() function.
So, the expression should be
=string(duration(process.GetCustomerAccounts.wait)+duration(process.GetCustomerAccounts.wait))
Or,
=string(duration(process.GetCustomerAccounts.wait)*2)
If this expression is used for a timer event then it can be used directly without the transformation.
Does this solve the issue?
Hi Philipp - yep - that was it. Awesome - thank you…