code: @Override
  	public boolean containsKey(final Object key) {
  		lock.readLock().lock();
  		try {
  			if (isKeyValid(key)) {
  				final boolean useLocalPrefixes = !mixDefaultAndLocalPrefixes && hasLocalPrefixConfigurations();
  				if (!properties.containsKey(getPrefixedKey(key, useLocalPrefixes))) {
  					return properties.containsKey(key);
  				} else {
  					return true;
  				}
  			}
  			return false;
  		} finally {
  			lock.readLock().unlock();
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see java.util.Hashtable#containsKey(java.lang.Object)