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Boolean result not accepted in a boolean variable

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Posted on by fsuarezoedt

I have a variable, initialized as boolean:

I try to set the value with a empty() function:

According to the documentation, the empty() function should give me a boolean answer:

But I get:

What is wrong with my formula?

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Building flows

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NathanAlvares24 1,714 Moderator on at

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Hi fsuarezoedt!

May I know what is the output of this? Does it return something? Please do provide a screenshot of the output of this:

outputs('Target')?['gs_fechavencimientodocumento'])

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faschimi 60 on at

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Did you try to remove string() function from the formula? It would be:
empty(outputs('Target')?['gs_fechavencimientodocumento'])

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Gopala_Krishna 1,495 on at

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You can try using the expression
null(string(outputs('Target')?['gs_fechavencimientodocumento']))

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fsuarezoedt 46 on at

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@gopala Krishna

But my question is WHY empty(), a function that should return a boolean value, can't be but on a boolean variable?

@fashimi

Yes, that worked, but didn't solve my question. WHY removing the string() changes the empty() behaviour? I mean, it's a boolean function, right? I should be able to put that function inside a boolean variable...

@NathanAlvarez24, it's a null

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David_MA 12,978 Super User 2025 Season 2 on at

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I am not sure about this since I cannot think of where I may have used an expression in a set variable action. If the action where you are having the issue is a create variable action, set the default to either true or false. Then use a set variable action with the expression above.

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faschimi 60 on at

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This guy says that empty() function cannot be nested, maybe this answers your question?
https://manueltgomes.com/reference/powerautomate-function-reference/power-automate-empty-function/

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fsuarezoedt 46 on at

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Sorry for the delay

The problem is that I forgot the 'body/' before the 'gs_fechavencimientodocumento'.

Now, using the complete value:

I get:

So the problem seems to be that I should be getting a meaningful error.

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