message: fix: avoid undefined strings
diff: @@ -68,7 +68,7 @@ function html(content, payload) {
  <!-- content.head -->
  ${content.head || ""}
  <!-- content.css -->
  - ${content.css}
  + ${content.css || ""}
  </head>
  <body>
  <!-- content.before -->
  @@ -78,7 +78,7 @@ function html(content, payload) {
  <!-- content.after -->
  ${content.after || ""}
  <textarea style="display:none" data-patternplate-vault="data-patternplate-vault">
  - ${data}
  + ${data || "{}"}
  </textarea>
  <script src="/api/patternplate-vendors.js"></script>
  <script src="/api/patternplate-components.js"></script>
  