Permalinks cause panic panic runtime error: slice bounds out of range [1:0]

I placed the following at the bottom of my config.toml file and it gives me this error: “panic: runtime error: slice bounds out of range [1:0]”.

[permalinks]
  [permalinks.page]
    posts = '/a/:slug/'
  [permalinks.section]
    posts = '/a/'

Which version of Hugo?

https://github.com/gohugoio/hugo/releases/tag/v0.115.0

Thank you! I had v0.111. I’m loving this new permalink option. It’s exactly what I’ve been looking for.