Merge pull request #1380 from aaronlehmann/avoid-empty-accept-header

Avoid empty Accept headers in client requests

manifests.go

@@ -69,8 +69,10 @@ type Describable interface {
 // ManifestMediaTypes returns the supported media types for manifests.
 func ManifestMediaTypes() (mediaTypes []string) {
 	for t := range mappings {
+		if t != "" {
 			mediaTypes = append(mediaTypes, t)
 		}
+	}
 	return
 }