The docs for FieldPath say

This method splits on the character . and disallows the characters ``*/[]. To create a FieldPath whose components have those characters, call the constructor.

When I try using a UUID string (ex: a344a6ea-9911-40a8-bd99-00f0b8d61155) it fails with:
"Non-alphanum char in element with leading alpha: {}"

The regex used is at