Symfony version(s) affected: 4.3.0 - 5.1.0

Description
When calling toArray() on a response with an empty body, a TransportException is thrown. A TransportException should be thrown on network errors. However, responses with empty body might be completely valid. In that case, toArray() should throw JsonException (or other exception that implements DecodingExceptionInterface) should be thrown, because the reponse body does not contain valid JSON.

How to reproduce

$httpClient = HttpClient::create();
$response = $httpClient->request('GET', 'https://httpbin.org/status/201');
$response->toArray(); // throws TransportException with message 'Response body is empty.'

Possible Solution
Throw a JsonException instead of a TransportException when response body is empty.