Merge branch 'master' into stable-6.7

* master:
  CommitGraphWriter: throw exception on unknown chunk

Change-Id: Iaa0c563917c4195fccd57f5e6839a37008c9b808

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/commitgraph/CommitGraphWriter.java

@@ -222,6 +222,9 @@ private void writeChunks(ProgressMonitor monitor,
 				}
 				chunk.data.get().writeTo(out);
 				break;
+			default:
+				throw new IllegalStateException(
+						"Don't know how to write chunk " + chunkId); //$NON-NLS-1$
 			}
 		}
 	}