Fix NPE in FS$FileStoreAttributeCache.getFsTimestampResolution

Bug: 548682
Change-Id: I48840d3a68cf1db92c056d218a0d5ed0b9ea4c45
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FSTest.java

@@ -65,6 +65,7 @@ import java.util.concurrent.TimeUnit;
 
 import org.eclipse.jgit.errors.CommandFailedException;
 import org.eclipse.jgit.junit.RepositoryTestCase;
+import org.eclipse.jgit.lib.RepositoryCache;
 import org.junit.After;
 import org.junit.Assume;
 import org.junit.Before;
@@ -223,4 +224,11 @@ public class FSTest {
 			}
 		}
 	}
+
+	// bug 548682
+	@Test
+	public void testRepoCacheRelativePathUnbornRepo() {
+		assertFalse(RepositoryCache.FileKey
+				.isGitRepository(new File("repo.git"), FS.DETECTED));
+	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java

@@ -218,6 +218,7 @@ public abstract class FS {
 				+ System.getProperty("java.vm.version") + '|'; //$NON-NLS-1$
 
 		private static Duration getFsTimestampResolution(Path file) {
+			file = file.toAbsolutePath();
 			Path dir = Files.isDirectory(file) ? file : file.getParent();
 			FileStore s;
 			try {