How can I clear or remove a session attribute in Lex using the Set Attributes block?

While there isn't a direct method to remove or nullify a session attribute using the Set Values block in Amazon Lex V2, you can use a workaround to effectively clear the attribute. Instead of trying to set the attribute to null, which doesn't work as expected, you can set the attribute to an empty string.

To clear or remove a session attribute in Lex V2 using the Set Values block, you can use the following syntax:

[SessionAttribute] = ""

This will set the value of the session attribute to an empty string, which for most practical purposes is equivalent to clearing the attribute. Your application can then check if the attribute is an empty string to determine if it has been cleared.

If you need to conditionally clear the attribute, you can use a condition in the Set Values block. For example:

[SessionAttribute] = #if(your_condition_here, "", [SessionAttribute])

This expression will set the attribute to an empty string if the condition is true, otherwise it will keep its current value.

Remember that session attributes in Lex V2 are identified using square brackets around the attribute name. While this method doesn't technically remove the attribute from the session, setting it to an empty string effectively clears its value and can be treated as removed in your bot's logic.

If you absolutely need to completely remove the attribute from the session (rather than just clearing its value), you would need to handle this in a custom Lambda function or in your client application using the Lex runtime API, as the Set Values block in the Lex console doesn't provide a direct way to remove attributes entirely.

Sources
Set values during the conversation - Amazon Lex
Understanding Amazon Lex V2 bot sessions - Amazon Lex