Update

update.sh

@@ -14,6 +14,13 @@ DOCKER_REGISTRY_HOST=${DOCKER_REGISTRY_HOST:-""}  # e.g. registry.example.com
 BASE_DIR="$( cd "$(dirname "$0")" && pwd )"
 source "${BASE_DIR}/versions.sh"
 
+# Fail if we push to hub
+if [ "${DOCKER_BUILD}" = "1" ] && [ "${DOCKER_PUSH}" = "1" ] && [ -z "${DOCKER_REGISTRY_HOST}" ]; then
+  echo "ERROR: DOCKER_REGISTRY_HOST is empty but DOCKER_PUSH=1. This would push to Docker Hub (docker.io)."
+  echo "Set DOCKER_REGISTRY_HOST to your registry or log in to Docker Hub explicitly if that is intended."
+  exit 1
+fi
+
 # If a target version is provided to the build script, only build this one
  if [ "$#" -ge  "1" ]
    then