code: private File getFile(final ConfigurationSourceKey key) {
  		final String fileName = getFileName(key);
  		if (externalConfigPath != null) {
  			final File f = new File(externalConfigPath, fileName);
  			if (f.exists())
  				return f; // return overwritten configuration location
  		}
  		
  		// configuration-file was not overwritten, so read from class path
  		final ClassLoader myLoader = getClass().getClassLoader();
  		final URL url = myLoader.getResource(fileName);
  		
  		return url == null ? null : new File(url.getFile());
  	}
docs: Determine a {@link File} handle related to given {@link ConfigurationSourceKey}. This method returns
  NULL if file does not exists - neither on file-system nor within a classpath-JAR-file.
  Keep in mind, if file is located within JAR, {@link File#exists()} will return FALSE.
  
  @param key
  {@link ConfigurationSourceKey}
  @return {@link File} related to given {@link ConfigurationSourceKey} or
  maybe NULL if no such configuration URL could be found.