n8n-docs/docs/code/cookbook/expressions/check-incoming-data.md

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howto

Check incoming data

At times, you may want to check the incoming data. If the incoming data doesn't match a condition, you may want to return a different value. For example, you want to check if a variable from the previous node is empty and return a string if it's empty. Use the following code snippet to return not found if the variable is empty.

{{$json["variable_name"]? $json["variable_name"] :"not found"}}

The above expression uses the ternary operator. You can learn more about the ternary operator here.