scottjehl/picturefill — pull request #158 by bryanburgers (2014-04-09 20:13:37+00:00)
Title: Only add img[alt] when [data-alt] exists

Fix a bug where, when the element specified by [data-picture] did not have
a [data-alt] attribute, the generated image element had would have an
[alt] attribute set to the string value "null".

```
→
```

Now, the following hold:

```
→
→
→
```