Fix NPE in HttpAuthMethod

If the password char array is null constructing a new String from this
array fails with a NPE. Add a null check to fix this.

Change-Id: Ifae6eecca38d5f114861f44658a32521e6e96866
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/HttpAuthMethod.java

@@ -219,7 +219,8 @@ abstract class HttpAuthMethod {
 			if (credentialsProvider.supports(u, p)
 					&& credentialsProvider.get(uri, u, p)) {
 				username = u.getValue();
-				password = new String(p.getValue());
+				char[] v = p.getValue();
+				password = (v == null) ? null : new String(p.getValue());
 				p.clear();
 			} else
 				return false;