if {[string length $checkoutDirectory] == 0} then {
      error [string map [list \
          %error% "checkout directory is invalid"] \
          $message]
    }

    if {![file isdirectory $checkoutDirectory]} then {
      error [string map [list %error% [appendArgs \
          "checkout directory \"" $checkoutDirectory \
          "\" is not really a directory"]] $message]
    }
  }

  #