When building flows in Power Automate, you’ll often find yourself needing to validate whether a value exists before taking action. A common use case is verifying if a field in your dynamic content is empty like checking whether an email message has a replyToId.
In this blog post, we’ll break down the empty() expression, explore a real-world example, and walk through best practices to avoid errors in your flows.
✅ The Use Case
Imagine you’re building a flow that processes incoming email messages. You only want to take action if the message is a reply to another email. To determine this, you check the replyToId field using the empty() function.
empty(outputs('Get_message_details')?['body/replyToId'])
🧩 Breaking It Down
Let’s dissect this expression step by step:
1. outputs(‘Get_message_details’)
This retrieves the output object from the action named “Get message details” in your flow.
2. ?[‘body/replyToId’]
The question mark ? is known as the safe navigation operator.
• It ensures the expression doesn’t break if replyToId is missing.
• If replyToId doesn’t exist, this will return null instead of throwing an error.
3. empty(…)
The empty() function checks if the value is:
• null
• An empty string (“”)
• An empty array ([])
So:
• If replyToId exists and has a value, empty() returns false.
• If it’s missing or empty, empty() returns true.
🧠 Pro Tips
• Always use the ? operator when accessing nested properties. It helps avoid flow failures.
• Combine empty() with other expressions like and(), or() for more complex logic.
• You can use coalesce() as a fallback to provide default values if needed.
📌 Conclusion
The empty() function is a simple but powerful tool when working with Power Automate. It lets you write safe, error-resistant flows that can gracefully handle missing data—especially in dynamic content like email fields.
By mastering empty() and the safe navigation operator, you’ll create more reliable and intelligent automations.
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