That variable is only used once, added as a value to a dictionary object.

The dictionary is used to set data into the document, but if there was an issue, I'd expect it to be a runtime error when that value is used if it's not the correct type (i.e. an object used where a string is expected), and even that is not the case.

The dictionary values are also written to the document variables collection (which is the only place that this specific constant is written), and a single is a valid type to write to a document variable.