fixed tests by prepending HTTP to URLs without protocol and adding a check for null.

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

@@ -2,6 +2,7 @@ package org.schabi.newpipe.extractor.services.youtube.linkHandler;
 
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.linkhandler.ListLinkHandlerFactory;
+import org.schabi.newpipe.extractor.utils.Utils;
 
 import java.net.URL;
 import java.util.List;
@@ -42,7 +43,7 @@ public class YoutubeChannelLinkHandlerFactory extends ListLinkHandlerFactory {
     @Override
     public String getId(String url) throws ParsingException {
         try {
-            URL urlObj = new URL(url);
+            URL urlObj = Utils.stringToURL(url);
             String path = urlObj.getPath();
 
             if (!(YoutubeParsingHelper.isYoutubeURL(urlObj) || urlObj.getHost().equalsIgnoreCase("hooktube.com"))) {

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

@@ -23,7 +23,7 @@ public class YoutubePlaylistLinkHandlerFactory extends ListLinkHandlerFactory {
     @Override
     public String getId(String url) throws ParsingException {
         try {
-            URL urlObj = new URL(url);
+            URL urlObj = Utils.stringToURL(url);
 
             if (!YoutubeParsingHelper.isYoutubeURL(urlObj)) {
                 throw new ParsingException("the url given is not a Youtube-URL");

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

@@ -58,13 +58,14 @@ public class YoutubeStreamLinkHandlerFactory extends LinkHandlerFactory {
     public String getId(String urlString) throws ParsingException, IllegalArgumentException {
         try {
             URI uri = new URI(urlString);
+            String scheme = uri.getScheme();
 
-            if (uri.getScheme().equals("vnd.youtube")) {
+            if (scheme != null && scheme.equals("vnd.youtube")) {
-                String scheme = uri.getSchemeSpecificPart();
+                String schemeSpecificPart = uri.getSchemeSpecificPart();
-                if (scheme.startsWith("//")) {
+                if (schemeSpecificPart.startsWith("//")) {
-                    urlString = "https:" + scheme;
+                    urlString = "https:" + schemeSpecificPart;
                 } else {
-                    return assertIsID(scheme);
+                    return assertIsID(schemeSpecificPart);
                 }
             }
         } catch (URISyntaxException ignored) {
@@ -72,7 +73,7 @@ public class YoutubeStreamLinkHandlerFactory extends LinkHandlerFactory {
 
         URL url;
         try {
-            url = new URL(urlString);
+            url = Utils.stringToURL(urlString);
         } catch (MalformedURLException e) {
             throw new IllegalArgumentException("The given URL is not valid");
         }
@@ -115,7 +116,7 @@ public class YoutubeStreamLinkHandlerFactory extends LinkHandlerFactory {
 
                     URL decodedURL;
                     try {
-                        decodedURL = new URL("http://www.youtube.com" + uQueryValue);
+                        decodedURL = Utils.stringToURL("http://www.youtube.com" + uQueryValue);
                     } catch (MalformedURLException e) {
                         throw new ParsingException("Error no suitable url: " + urlString);
                     }

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

@@ -21,6 +21,7 @@ package org.schabi.newpipe.extractor.services.youtube.linkHandler;
  */
 
 import org.schabi.newpipe.extractor.linkhandler.ListLinkHandlerFactory;
+import org.schabi.newpipe.extractor.utils.Utils;
 
 import java.net.MalformedURLException;
 import java.net.URL;
@@ -41,7 +42,7 @@ public class YoutubeTrendingLinkHandlerFactory extends ListLinkHandlerFactory {
     public boolean onAcceptUrl(final String url) {
         URL urlObj;
         try {
-            urlObj = new URL(url);
+            urlObj = Utils.stringToURL(url);
         } catch (MalformedURLException e) {
             return false;
         }

extractor/src/main/java/org/schabi/newpipe/extractor/utils/Utils.java

@@ -3,6 +3,7 @@ package org.schabi.newpipe.extractor.utils;
 import org.schabi.newpipe.extractor.exceptions.ParsingException;
 
 import java.io.UnsupportedEncodingException;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLDecoder;
 import java.util.List;
@@ -43,7 +44,7 @@ public class Utils {
     }
 
     public static void printErrors(List<Throwable> errors) {
-        for(Throwable e : errors) {
+        for (Throwable e : errors) {
             e.printStackTrace();
             System.err.println("----------------");
         }
@@ -55,7 +56,7 @@ public class Utils {
     public static String replaceHttpWithHttps(final String url) {
         if (url == null) return null;
 
-        if(!url.isEmpty() && url.startsWith(HTTP)) {
+        if (!url.isEmpty() && url.startsWith(HTTP)) {
             return HTTPS + url.substring(HTTP.length());
         }
         return url;
@@ -99,4 +100,24 @@ public class Utils {
 
         return null;
     }
+
+    /**
+     * converts a string to a URL-Object.
+     * defaults to HTTP if no protocol is given
+     *
+     * @param url the string to be converted to a URL-Object
+     * @return a URL-Object containing the url
+     */
+    public static URL stringToURL(String url) throws MalformedURLException {
+        try {
+            return new URL(url);
+        } catch (MalformedURLException e) {
+            // if no protocol is given try prepending "http://"
+            if (e.getMessage().equals("no protocol: " + url)) {
+                return new URL(HTTP + url);
+            }
+
+            throw e;
+        }
+    }
 }