Can't use ~ in refname projection to mean unversioned

As described in #users > ✔️ Setting the version to unversioned in a refname project... I tried use a refname projection with ~ to mean "unversioned":

This led to a literal ~ as the version:

version:
  (?<version>+({0..9}).+({0..9})): $<version>
  dev/rn/(*): $1
  release/rn: '~'

This led to an error FATAL (antora): Cannot read properties of null (reading 'replace')...:

version:
  (?<version>+({0..9}).+({0..9})): $<version>
  dev/rn/(*): $1
  release/rn: ~

A workaround is to use an empty string:

version:
  (?<version>+({0..9}).+({0..9})): $<version>
  dev/rn/(*): $1
  release/rn: ''