JSONPath表达式[=],报错

在1.2.83版本中可以 2.0.40版本不可以

```
Person person = new Person();
person.setId("1");
person.setAge(10);
Object eval = JSONPath.eval(person, "[age=10]");
System.out.println("eval = " + eval);
```

Start with the JSONPath.eval entry point and reproduce the supplied Java snippet in fastjson2 2.0.40, comparing it with 1.2.83. Trace why the [age=10] expression errors in the newer version; done means the expression evaluates successfully as it did in 1.2.83.

Written by the indexing model from the issue text.