private static <T> T parseJsonString(String content, TypeReference<T> typeReference)
            throws GraphqlWebSocketCloseException {
        try {
            return mapper.readValue(content, typeReference);
        } catch (JsonProcessingException e) {
            throw new GraphqlWebSocketCloseException(4400, "Invalid JSON");
        }
    }
This only works reliably if maybeMap is from Json, as maps(objects) in Json
can only have string keys.
graphql/src/main/java/com/linecorp/armeria/server/graphql/GraphqlWSSubProtocol.java