Add tests for newly supported channel URLs and fix regression

Author: G-flat

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/linkHandler/YoutubeChannelLinkHandlerFactory.java

@@ -71,7 +71,8 @@ public String getUrl(final String id,
      * @return whether the value conform to short channel URLs
      */
     private boolean isCustomShortChannelUrl(@Nonnull final String[] splitPath) {
-        return splitPath.length == 1 && !EXCLUDED_SEGMENTS.matcher(splitPath[0]).matches();
+        return splitPath.length == 1 && !splitPath[0].isEmpty()
+                && !EXCLUDED_SEGMENTS.matcher(splitPath[0]).matches();
     }
 
     /**

extractor/src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelLinkHandlerFactoryTest.java

@@ -88,5 +88,8 @@ void getIdFromUrl() throws ParsingException {
 
         assertEquals("@Gronkh", linkHandler.fromUrl("https://www.youtube.com/@Gronkh?ucbcb=1").getId());
         assertEquals("@YouTubeCreators", linkHandler.fromUrl("https://www.youtube.com/@YouTubeCreators/shorts").getId());
+
+        assertEquals("PewDiePie", linkHandler.fromUrl("https://www.youtube.com/PewDiePie").getId());
+        assertEquals("DreamTraps", linkHandler.fromUrl("https://www.youtube.com/DreamTraps").getId());
     }
 }