Tip - How to set up a Condition in Power Automate flow to check if "the field is empty"

Tip - How to set up a Condition in Power Automate flow to check if "the field is empty"

  September 29, 2021    afei2046

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Scenario:

sometimes, we have to check if the field contain data or is empty under the Condition action in a Power Automate flow, and we may be confused about which expression should be used to set up the condition.

Reference material from Microsoft

If you use logical functions or conditions to compare values, null values are converted to empty string ("") values. The behavior of conditions differs when you compare with an empty string instead of a null value. For more information, see the string() function.

Refer to below link for more details from Microsoft:

https://docs.microsoft.com/en-us/azure/logic-apps/workflow-definition-language-functions-reference#logical-comparison-functions

"empty" function

Check whether a collection is empty. Return true when the collection is empty, or return false when not empty.

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empty('<collection>')empty([<collection>])

Parameter	Required	Type	Description
<collection>	Yes	String, Array, or Object	The collection to check

Return value	Type	Description
true or false	Boolean	Return true when the collection is empty. Return false when not empty.

Example

These examples check whether the specified collections are empty:

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empty('')empty('abc')

And returns these results:

• First example: Passes an empty string, so the function returns true.
• Second example: Passes the string "abc", so the function returns false.

Refer to below link for more details from Microsoft:

https://docs.microsoft.com/en-us/azure/logic-apps/workflow-definition-language-functions-reference#empty

On the left side of the condition

"empty" function

empty([DynamicValue])e.g. empty(triggerOutputs()?['body/address1_city'])

but please note that the type of DynamicValue should be String, Array, or Object only (most of time, it will be a string type), otherwise, you will see an error, for instance, if we try to use a option set (choice) field in the Empty function indicated below, then we will see below error message during the run.

e.g.empty(triggerOutputs()?['body/preferredcontactmethodcode'])

"length" function

length([DynamicValue])e.g.length(outputs('retrieve_option')?['body/methodToUpdate'])

but please note that the type of DynamicValue should be String, Array only. for instance, you can use it to check the length of an array in order to verify if the file or option exists. If it’s greater than 0, the array is not empty. If it’s 0, then it’s empty.

On the right side of the condition

If you intend to check if a field is empty or not (on the right side of the condition) , and then do something. there are also couple of ways you can refer to.

null keyword

Just open the expression builder as below pic shown, and enter null, then you will see below predefined value “null” show up, after that, you can just click on Update to add it in the condition on the right side for comparison.

empty string ("") value

if you‘re sure that the data type of the field you’re using on the left side of the condition is a string, then you can just put empty string on the right side for comparison.