message: Return error on empty front matter
diff: @@ -177,6 +177,10 @@ impl Document {
  let yaml_result = try!(YamlLoader::load_from_str(attribute_split));
  + if yaml_result.is_empty() {
  + return Err(format!("Incorrect front matter format in {:?}", file_path).into());
  + }
  +
  let yaml_attributes = try!(yaml_result[0]
  .as_hash()
  .ok_or_else(|| format!("Incorrect front matter format in {:?}", file_path)));
  