FeelEngine not handling null values for list functions

BPMN & Modeling Discussion & Questions
1

Hi there,

I am currently using FEEL built in list functions, specifically max and min. It works fine when all values exist i.e. are not null, but when a value is null it cannot execute.

Example:
max(null, 0.5, 0.5)
has error of:
ValNull is not allowed
ValList(List(ValNull, ValNumber(0.5), ValNumber(0.5))) is not comparable

I would expect the default behaviour to just ignore null values and compare any of the remaining values…

2

Hi @phoebe

List maintains a list of object references. Object references can either be a reference to a valid, extant object, or null to indicate that they don’t currently contain an object reference.

If you try to invoke methods/variables on that resulted null , then you run into exception.

Hope it helps !

Thanks
Anmol

3

I see your point and agree that it would be handy. But according to the DMN spec, I don’t think that this expectation is correct. The function min()/max() expects a non-empty list of comparable items. But null is not comparable.

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image931×137 8.66 KB

(DMN 1.3 page 160)

Note that you could filter the list and remove all null values. For example, by using the expression:

myValues[item != null]

Does this help you?