src/Http/Formatting/HttpBodyParser.php
public function readAsJson(?IHttpBody $body): array
    {
        if ($body === null) {
            return [];
        }

        $json = json_decode($body->readAsString(), true);

        if ($json === null) {
            throw new RuntimeException('Body could not be decoded as JSON');
        }

        return $json;
    }
public function readAsJson(?IHttpBody $body): array
    {
        if ($body === null) {
            return [];
        }

        $json = json_decode($body->readAsString(), true);

        if ($json === null) {
            throw new RuntimeException('Body could not be decoded as JSON');
        }

        return $json;
    }
Attempts to read the request body as JSON

@param IHttpBody|null $body The body to parse
@return array The request body as JSON
@throws RuntimeException Thrown if the body could not be read as JSON