fix: prevent unbound variable error

abra.sh

@@ -1,2 +1,2 @@
-export ENTRYPOINT_CONF_VERSION=v11
+export ENTRYPOINT_CONF_VERSION=v12
 export PG_BACKUP_VERSION=v1

compose.postgresql.yml

@@ -2,7 +2,6 @@ version: "3.8"
 services:
   app:
     environment:
-      - POSTGRES_ENABLED=1
       - CMD_DB_NAME=codimd
       - CMD_DB_USER=codimd
       - CMD_DB_HOST=db

entrypoint.sh.tmpl

@@ -22,13 +22,15 @@ file_env() {
 }
 
 load_vars() {
-  file_env "CMD_DB_PASSWORD"
+  if [ -n "${CMD_DB_PASSWORD}" ] ; then
+    file_env "CMD_DB_PASSWORD"
+  fi
   file_env "CMD_OAUTH2_CLIENT_SECRET"
   file_env "CMD_SESSION_SECRET"
 }
 
 main() {
-  set -eu
+  set -e
 
   load_vars
   mkdir -p "/hedgedoc/.npm" && \
@@ -40,8 +42,9 @@ main() {
 
 main
 
-if [ -n "$POSTGRES_ENABLED" ]; then
-export CMD_DB_URL="postgres://$CMD_DB_USER:$CMD_DB_PASSWORD@$CMD_DB_HOST:5432/$CMD_DB_NAME"
+if [ -z "${CMD_DB_URL}" ] ; then
+  # TODO: support databases other than postgres and sqlite
+  export CMD_DB_URL="${postgres://$CMD_DB_USER:$CMD_DB_PASSWORD@$CMD_DB_HOST:5432/$CMD_DB_NAME}"
 fi
 
 # 3wc: `source /docker-entrypoint.sh -e` to load CMD_DB_URL for CLI scripts
@@ -52,4 +55,4 @@ if [ ! "${1-}" == "-e" ]; then
   /usr/local/bin/docker-entrypoint.sh npm start
 fi
 
-set +eu
+set +e