Describe the problem/error/question
I want to remove the assignee field or value when there is undefined in the following node :
Currently I’m getting
NodeOperationError: ERROR: Assignee parameter's value is invalid. Please enter a valid ID.
Hey @QuantumSheep,
Welcome to the community 
Best option there would be 2 nodes one with assignee and one without then use an if node to work out which one needs to be used. It could be that the jira api allows a value to be set with something like undefined or null but I suspect you have tried that already so I would take the 2 node approach.
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Hey, thanks for you answer!
Yes I’ve tried undefined and null without success 
I guess the only presence of assignee makes the Jira API to check validity for this field.
I implemented a fix for this issue.
The PR looks ok and if I am reading it right if a non required field has no value set it won’t send it, In theory that is good but I think that might actually break some functionality. As it is a core change though it will need to go to a different team to review so for now the best solution is still going to be using 2 nodes 
My thought on this which I was writing up as a feature request was to have a property for fields that can be set to only be sent if not empty or if an expression validates this would open a lot more doors for other things.
We could add an optional field instead of using required === false to mitigate any breaking changes.
There is a hacky workaround for this. Using the custom fields option you can enter any standard field name like summary, assignee, reporter. Then just use an expression {{ null }} for the value.
I get the following error:
ERROR: Bad request - please check your parameters
400 - {"errorMessages":[],"errors":{"assignee":"data was not an object"}}
Can you post a screenshot of your config? Or the workflow JSON
