How to block downstream components if an imput is empty



I’d like this “Concatenate” not to output anything if one of the inputs is empty.
I guess I need to transform a valid input into a “True” and an empty input into a “Null” and the use a “Stream filter” component.
I’m perplexed by the subtleties between a “Null” and “Empty” and “No data was collected” item in a list…

(Lando Schumpich) #4

Not on a PC right now so can’t try it out but maybe ‘list length’ -> ‘expression (if x=0,0,1)’ will do the trick


OK, this works with “No data collected” :

… and “Nothing” (There are too many flavors of nothingness !!!)

(Giulio Piacentino) #6

Are you OK with the solution you found, @osuire?


Hi Giulio,

Well, it seems to work, although I think that there should be an option on component inputs to deal with this.
See, when there are multiple inputs in certain components, there will still be an output even if one of the inputs is “empty”.
There could be an option on the input saying something like : “If this input is empty, there should be no output”.

I need to point out that the nuance between a “blank” , a “null” , an “Empty” and a “No data was collected” value in a list leaves me perplexed.
Is it really important to make such nuances ? Shouldn’t there be an easy way to drive what should happen next when each one of these cases is encountered ?

The case of “Null” seems to be covered, but as I discovered here, the others don’t seem to be.

(Giulio Piacentino) #8

Well those wordings are for Tree with no branches, Tree with branches and no items, Tree with branches and empty items… etc. @DavidRutten can explain more.


I remember a post where he explained this quite well, but it would be nice to find this in documentation.

(Matt Gaydon) #10

Does this work as you would like it too.

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