Clean up undefined classes

Author: josh-collinsworth

_components/Header.tsx

@@ -12,7 +12,7 @@ export default function (data: Lume.Data) {
         {data.navigation.map((nav: NavData) => (
           <a
             href={nav.href}
-            className={`header-nav-link blocklink ${nav.style}`}
+            className={`header-nav-link blocklink ${nav.style ?? ""}`}
             {...(nav.href.includes(data.currentSection)
               ? { "data-active": true, "aria-current": "location" }
               : {})}