Your code is likely to be affected if you use auto to store the result of operator[]. For example, the following line won't compile anymore:

auto value = doc["key"];

To fix the issue, you must append either .as<T>() or .to<T>(), depending on the situation.

For example, if you are extracting values from a JSON document, you should update like this:

- auto config = doc["config"];
+ auto config = doc["config"].as<JsonObject>();
const char* name = config["name"];

However, if you are building a JSON document, you should update like this:

- auto config = doc["config"];
+ auto config = doc["config"].to<JsonObject>();
config["name"] = "ArduinoJson";

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