Current directory not shown if DIR is unset

[romkatv]

This is on master.

docker run -e LANG=C.UTF-8 -e LC_ALL=C.UTF-8 -e TERM -it --rm ubuntu bash -uexc '
  cd
  apt update && apt install -y zsh git
  git clone https://github.com/bhilburn/powerlevel9k.git
  echo "source ~/powerlevel9k/powerlevel9k.zsh-theme; unset PWD" >~/.zshrc
  exec zsh'

Actual:

Expected:

I know it's weird to unset PWD but it happens. Basic zsh prompt still shows the current directory in this case, so it's not entirely unreasable to expect it.