Minor fix

src/views/frontpage.js

@@ -7,7 +7,7 @@ const date = `${new Date().toISOString().split('.')[0]}Z`;
 // Render the frontpage cards, with href and imageurl
 const renderCards = item => {
   const { title, href } = item;
-  const imageurl = item.img_infoscreen ? `${apiUrl}${item.img_infoscreen.file}` : null;
+  const imageurl = item.img_infoscreen ? `${apiUrl}${item.img_infoscreen.file}` : '';
   return m(
     'div.frontpage-card',
     { style: `background-image: url(${imageurl})` },
@@ -18,7 +18,7 @@ const renderCards = item => {
 // Render the Hot Cards, with link and imageurl
 const renderHotCards = (item, index) => {
   const { title, href } = item;
-  const imageurl = item.img_infoscreen ? `${apiUrl}${item.img_infoscreen.file}` : null;
+  const imageurl = item.img_infoscreen ? `${apiUrl}${item.img_infoscreen.file}` : '';
   if (index === 0) {
     return m(
       'div.hot-first-card',