[MediaCCC] Return null instead of empty items collector

As per the documentation in the base getRelatedStreams()

extractor/src/main/java/org/schabi/newpipe/extractor/services/media_ccc/extractors/MediaCCCStreamExtractor.java

@@ -219,7 +219,7 @@ public class MediaCCCStreamExtractor extends StreamExtractor {
 
     @Override
     public StreamInfoItemsCollector getRelatedStreams() {
-        return new StreamInfoItemsCollector(getServiceId());
+        return null;
     }
 
     @Override

extractor/src/test/java/org/schabi/newpipe/extractor/services/media_ccc/MediaCCCStreamExtractorTest.java

@@ -53,6 +53,7 @@ public class MediaCCCStreamExtractorTest {
         @Nullable @Override public String expectedTextualUploadDate() { return "2018-05-11T02:00:00.000+02:00"; }
         @Override public long expectedLikeCountAtLeast() { return -1; }
         @Override public long expectedDislikeCountAtLeast() { return -1; }
+        @Override public boolean expectedHasRelatedStreams() { return false; }
         @Override public boolean expectedHasSubtitles() { return false; }
         @Override public boolean expectedHasFrames() { return false; }
 
@@ -114,6 +115,7 @@ public class MediaCCCStreamExtractorTest {
         @Nullable @Override public String expectedTextualUploadDate() { return "2020-01-11T01:00:00.000+01:00"; }
         @Override public long expectedLikeCountAtLeast() { return -1; }
         @Override public long expectedDislikeCountAtLeast() { return -1; }
+        @Override public boolean expectedHasRelatedStreams() { return false; }
         @Override public boolean expectedHasSubtitles() { return false; }
         @Override public boolean expectedHasFrames() { return false; }