Use fallback value for parameter vars

.circleci/config.yml

@@ -119,7 +119,7 @@ workflows:
   weekly:
     triggers:
       - schedule:
-          cron: "26 15 * * 4"
+          cron: "34 15 * * 4"
           filters:
             branches:
               only:

docker/rebuild.sh

@@ -16,7 +16,7 @@ SUPPORTED_BRANCH_NAMES=("master")
 SUPPORTED_TAG_PATTERNS=("^v2.1.\([6789]\|1[0-9]\)$")
 IMAGE_NAME=threema/threema-web
 
-if [ $1 == "--dry-run" ]; then
+if [ ${1:-} == "--dry-run" ]; then
     echo -e "Dry run\n"
     DOCKER='echo > docker'
 else