Azure Logic App - simple condition to check for empty string variable fails

Question

Solved

Issue was due to error in child action as Thomas pointed out, not the way I was checking the variable value.

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I've got a variable that's been initialized earlier in the LA. Later on I'm trying to check if the variable is empty using a condition.

Here's the output from the run history:

It looks like the variable is an empty string at this point, however the condition fails without any helpful information.

I've also tried null or wrapping the variable in the empty command and comparing to true/false. All gave the same failure.

Belgium

Can you try something like that :@length(if(equals(triggerOutputs()?['headers']?['SAS-Uri'], null), '', triggerOutputs()?['headers']?['SAS-Uri'])) – Sabian

@Sabian - tried it but no luck. Are the ?'s like null conditional operators in c#? – Belgium

Yes the ? Is a null propagation operator – Sabian

The error message said that another action failed. Have you check your workflow ? It sounds like a child action is failing – Sabian

Ah, that was the problem. I assumed it was the condition action causing the problem, but it was a child action. I need to pay better attention to the message. Thanks! – Belgium

Good to here. you should edit your question or close it if it is not really relevant for the community. – Sabian

Answer 1

You can use the length function in the expression. I've found it helpful to also coallesce the value to an empty string before checking length.

Inhabited

Okay, here's what I've got now, but still getting the same error. This is a http trigger LA and I'm getting the value from the headers, btw. I've initialized the variable like so: coalesce(triggerOutputs()['headers']['SAS-Uri'], ''). Then in my condition I've got length(variables('SasUri')) with a greather than 0. – Belgium

Problem here is if you get null in the string that it will get an error. So be careful. – Alarice

Answer 2

For me placing an empty string between double quotes in a condition action to recognize the empty string works well. Be aware however that once you enter the empty string in the condition action and save your logic app, if you afterwards go back in the designer and reopen the condition action the empty string enclosed in double quotes ("") is not displayed anymore.

Laverne

This worked well for me. One of the only times to use double quotes in PowerAutomate/Logic Apps. – Leo

Answer 3

I have done this in 2 step process: Step 1: In compose connector If(equals(items('For_each')?['Email'],null), '',items('For_each')?['Email'])

Step 2: in Condition connector length(outputs('Email-EmptyOrNull')) is equal ZERO?

It works for me.

Matins