WWW Get Request with credentials not working anymore in Unity 2017.1.0f3

So, what we have since Unity 4 is following code:

string url = "https://www.domain.com/test.php?var1=value1&var2=value2"; 
string credentials = "user:pass";

Dictionary<string, string> headers = new Dictionary<string, string>() { { "Authorization", "Basic " + System.Convert.ToBase64String(System.Text.Encoding.ASCII.GetBytes(credentials)) } };

WWW www = new WWW(url, null, headers);
yield return www;

if (www.error != null) {
    // error handling
    Debug.LogWarning (string.Format ("Error: {0}", www.error));
    yield break;
}

// work with www result

It’s a bit simplified, the url is %-escaped.

This worked fine from unity 4 to 5.6.2, but is not working anymore in unity 2017.1.0f3.
Now it throws an error without an error message.

What has changed there?

Thanks!

Ok, i got it. Stupid mistake. They changed that the error-message is not null anymore, now it is an empty string. So there was not really an error, but it did the error handling and jumped out of the ienumerator. Testing with !string.IsNullOrEmpty() solved it.