@Override
    public Void visitModifyBackendClause(ModifyBackendClause clause, ConnectContext context) {
        if (clause.getBackendHostPort() == null) {
            checkModifyHostClause(clause.getSrcHost(), clause.getDestHost());
        } else {
            SystemInfoService.validateHostAndPort(clause.getBackendHostPort(), false);
            analyzeBackendProperties(clause.getProperties());
        }
        return null;
    }
@Test
    public void testVisitModifyBackendClause() {
        mockNet();
        AlterSystemStmtAnalyzer visitor = new AlterSystemStmtAnalyzer();
        ModifyBackendClause clause = new ModifyBackendClause("test", "fqdn");
        Void result = visitor.visitModifyBackendClause(clause, null);
    }