[findBugs] Fix potential NPE in CleanFilter

Change-Id: Ibc20e9fc16be62f61748b3f59f6d70c1ebf63671
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/CleanFilter.java

@@ -151,7 +151,10 @@ public class CleanFilter extends FilterCommand {
 						FileUtils.delete(tmpFile.toFile());
 					}
 				} else {
-					FileUtils.mkdirs(mediaFile.getParent().toFile(), true);
+					Path parent = mediaFile.getParent();
+					if (parent != null) {
+						FileUtils.mkdirs(parent.toFile(), true);
+					}
 					FileUtils.rename(tmpFile.toFile(), mediaFile.toFile(),
 							StandardCopyOption.ATOMIC_MOVE);
 				}