[findBugs] Fix NP_LOAD_OF_KNOWN_NULL_VALUE

The code analyzer can't know that passing a value known to be null is
not a problem. Hence better pass null explicitly instead of the
parameters being null.

Change-Id: I8db6f8014de6c00dd95974d60f61ecc66191e6d4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java

@@ -406,7 +406,7 @@ public class DirCacheCheckout {
 			// File/Directory conflict case #20
 			if (walk.isDirectoryFileConflict())
 				// TODO: check whether it is always correct to report a conflict here
-				conflict(name, null, h, m);
+				conflict(name, null, null, null);
 
 			// file only exists in working tree -> ignore it
 			return;