@Override
    public ExprNode parseValue(String value) throws GuacamoleException {

        // No value provided, so return null.
        if (value == null)
            return null;

        try {
            return FilterParser.parse(value);
        }
        catch (ParseException e) {
            throw new GuacamoleServerException("\"" + value + "\" is not a valid LDAP filter.", e);
        }

    }
A GuacamoleProperty with a value of an ExprNode query filter.  The string
provided is passed through the FilterParser returning the ExprNode object,
or an exception is thrown if the filter is invalid and cannot be correctly
parsed.
extensions/guacamole-auth-ldap/src/main/java/org/apache/guacamole/auth/ldap/conf/LdapFilterGuacamoleProperty.java