private static List<File> checkSpecificationFiles(String spec) throws PropertyException {
        if (spec == null || spec.isEmpty())
            throw new PropertyException("Missing property: config.spec");

        var files = new ArrayList<File>();
        for (String token : spec.split(",", -1)) {
            File file = new File(token);
            if (!file.isFile()) {
                throw new PropertyException("Could not read file " + file);
            }
            files.add(file);
        }

        return files;
    }
Encapsulates data extracted from system properties.

@author gjoranv
configgen/src/main/java/com/yahoo/config/codegen/MakeConfigProperties.java