private static String checkDirInRoot(File destDir,  String dirInRoot) throws PropertyException {
            // Optional parameter
        if (dirInRoot == null) { return null; }
        File f = new File(destDir, dirInRoot);
        if (!f.isDirectory()) {
            throw new PropertyException("Could not find directory: " + f.getPath());
        }
        return dirInRoot;
    }
Encapsulates data extracted from system properties.

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