public static Date loadTimestamp(File tsFile) throws IOException {
        try {
            if (tsFile.exists()) {
                String ts = FileUtils.fileRead(tsFile);
                return new Date(Long.parseLong(ts));
            } else {
                return null;
            }
        } catch (IOException e) {
            throw new IOException("Cannot read timestamp " + tsFile,e);
        }
    }
Return the first non null registry given. Use the env var DOCKER_REGISTRY as final fallback
@param checkFirst list of registries to check
@return registry found or null if none.
src/main/java/io/fabric8/maven/docker/util/EnvUtil.java