According to the spec, file inputs with files attached should be serialized with special values. However, plugins that specialize in uploading files, such as jQuery File Upload, handle serializing file inputs for us and they do it in ways that are able to take advantage of some HTML5 features when available. In other words, I think all we need to do is what we did before 1.9, which was ignore file inputs in serialization.

This test case demonstrates the difference in serialization between 1.8 and 1.9 and shows that the value is still empty string when files are attached.