Handle missing $1 in _autoenv_hash_pair

autoenv.zsh

@@ -122,12 +122,18 @@ _autoenv_debug() {
 zmodload -F zsh/stat b:zstat
 
 
+# Generate hash pair for a given file ($1).
+# A fixed hash value can be given as 2nd arg, but is used with tests only.
 _autoenv_hash_pair() {
   local env_file=${1:A}
   local env_shasum
   if [[ -n $2 ]]; then
     env_shasum=$2
   else
+    if ! [[ -e $env_file ]]; then
+      echo "Missing file argument for _autoenv_hash_pair!" >&2
+      return 1
+    fi
     env_shasum=$(shasum $env_file | cut -d' ' -f1)
   fi
   echo "$env_file:$env_shasum:1"