public void setAttribute(String login, String attr, String newValue) throws Exception, NullPointerException
public void setAttribute(String login, String attr, boolean newValue) throws SVNException, Exception, NullPointerException
	public void setAttribute(String login, String attr, String newValue) throws Exception, NullPointerException	{		XPath xpath = XPathFactory.newInstance().newXPath();		String expression = "//user[@login='"+login+"']";		Element elem = null;				try {			elem = (Element)xpath.evaluate(expression, this.doc, XPathConstants.NODE);		}		catch (XPathExpressionException e) {			ErrorManager.getInstance().setErrTitle("Expression XPath Incorrecte");			ErrorManager.getInstance().setErrMsg("Expression XPath "+ expression +" Incorrecte");			throw new XPathExpressionException(expression);		}		if ( elem != null ) {			if (attr == ATTR_LOGIN || attr == ATTR_PASSWD){				elem.setAttribute(attr, newValue);									saveDocument(usersXML);			}		}		else {			ErrorManager.getInstance().setErrTitle("Utilisateur inconnu");			ErrorManager.getInstance().setErrMsg("L'utilisateur "+ login +" est inconnu.\n");			throw new NullPointerException(); 		}	}