PackExtBlockCacheTableTest: fix empty block warning

Change-Id: I35e7527c6c555cd57fce14889412fa2fd6beab88

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTableTest.java

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTableTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTableTest.java
index d904946..8c003e0 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTableTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/PackExtBlockCacheTableTest.java
@@ -95,6 +95,7 @@ public void getOrLoad_packExtMapsToCacheTable_callsBitmapIndexCacheTable()
 			throws Exception {
 		BlockBasedFile blockBasedFile = new BlockBasedFile(null,
 				mock(DfsPackDescription.class), PackExt.BITMAP_INDEX) {
+			// empty
 		};
 		DfsBlock dfsBlock = mock(DfsBlock.class);
 		DfsBlockCacheTable defaultBlockCacheTable = mock(
@@ -125,6 +126,7 @@ public void getOrLoad_packExtDoesNotMapToCacheTable_callsDefaultCache()
 			throws Exception {
 		BlockBasedFile blockBasedFile = new BlockBasedFile(null,
 				mock(DfsPackDescription.class), PackExt.PACK) {
+			// empty
 		};
 		DfsBlock dfsBlock = mock(DfsBlock.class);
 		DfsBlockCacheTable defaultBlockCacheTable = mock(