Allow alternate host url in tracker.

lib/url.js

@@ -1,11 +1,11 @@
 export function removeTrailingSlash(url) {
-  return url.length > 1 && url.endsWith('/') ? url.slice(0, -1) : url;
+  return url && url.length > 1 && url.endsWith('/') ? url.slice(0, -1) : url;
 }
 
 export function getDomainName(str) {
   try {
     return new URL(str).hostname;
-  } catch {
+  } catch (e) {
     return str;
   }
 }