Fix test about exception type: NPE, not IllegalArgment

The relevant change was made in #877

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

@@ -24,7 +24,7 @@ public class YoutubeCommentsLinkHandlerFactoryTest {
 
     @Test
     public void getIdWithNullAsUrl() {
-        assertThrows(IllegalArgumentException.class, () -> linkHandler.fromId(null));
+        assertThrows(NullPointerException.class, () -> linkHandler.fromId(null));
     }
 
     @Test