code: @Override
  	public String getPrefixPart(final String key) {
  		if (key != null) {
  			lock.readLock().lock();
  			try {
  				for (final String prefixString : prefixes) {
  					if (key.startsWith(prefixString + getPrefixDelimiter())) {
  						return prefixString + getPrefixDelimiter();
  					}
  				}
  			} finally {
  				lock.readLock().unlock();
  			}
  			return "";
  		}
  		throw new IllegalArgumentException("The given key is null.");
  	}
docs: /*
  (non-Javadoc)
  
  @see
  net.sf.prefixedproperties.config.PrefixConfig#getPrefixPart(java.lang.
  String)