[BUGFIX] Show available firmware information

lib/infobox/node.js

@@ -27,14 +27,12 @@ define(['sorttable', 'snabbdom', 'd3-interpolate', 'moment', 'helper'],
     }
 
     function showFirmware(d) {
-      var release = helper.dictGet(d.nodeinfo, ['software', 'firmware', 'release']);
-      var base = helper.dictGet(d.nodeinfo, ['software', 'firmware', 'base']);
-
-      if (release === null || base === null) {
-        return undefined;
-      }
-
-      return release + ' / ' + base;
+      return [
+        helper.dictGet(d.nodeinfo, ['software', 'firmware', 'release']),
+        helper.dictGet(d.nodeinfo, ['software', 'firmware', 'base'])
+      ].filter(function (n) {
+        return n !== null;
+      }).join(' / ') || undefined;
     }
 
     function showSite(d, config) {