private static Class<?> declaringClassOf(TypeVariable<?> typeVariable) {
        GenericDeclaration genericDeclaration = typeVariable.getGenericDeclaration();
        return genericDeclaration instanceof Class
                ? (Class<?>) genericDeclaration
                : null;
    }
Returns the declaring class of {@code typeVariable}, or {@code null} if it was not declared by
a class.
core/src/main/java/com/alibaba/fastjson2/util/BeanUtils.java