数据中要合并的值全为空，报StringIndexOutOfBoundsException异常

[lookupman]

result.stream().forEach((obj) -> {
field.setAccessible(true);
Object o = null;

                    try {
                        o = field.get(obj);
                        if (o != null && !ids.contains(o)) {
                            ids.add(o.toString());
                            sb.append(o.toString()).append(",");
                        }

                    } catch (IllegalAccessException var6) {
                        log.error("数据属性加工失败:" + field, var6);
                        throw new RuntimeException("数据属性加工失败:" + field, var6);
                    }
                });
                args = sb.substring(0, sb.length() - 1);

如果sb为空，报如下异常StringIndexOutOfBoundsException: String index out of range: -1