message: feat(tags): Allow overriding default tag
  Because "no tags" is `None` and "no preference" is `one`, we need to
  allow `[]` to also represent `no tags` and convert it to `None`.
diff: @@ -430,6 +430,11 @@ impl FrontmatterBuilder {
  return Err("Empty strings are not allowed in tags".into());
  }
  }
  + let tags = if tags.as_ref().map(|t| t.len()).unwrap_or(0) == 0 {
  + None
  + } else {
  + tags
  + };
  let fm = Frontmatter {
  permalink,
  