PushCommand: do not set a null credentials provider

PushCommand now does not set a null credentials provider on
Transport because in this case the default provider is replaced with
null and the default mechanism for providing credentials is not
working.

Bug: 336023
Change-Id: I7a7a9221afcfebe2e1595a5e59641e6c1ae4a207
Signed-off-by: Jens Baumgart <jens.baumgart@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/PushCommand.java

@@ -139,6 +139,7 @@ public class PushCommand extends GitCommand<Iterable<PushResult>> {
 				if (receivePack != null)
 					transport.setOptionReceivePack(receivePack);
 				transport.setDryRun(dryRun);
+				if (credentialsProvider != null)
 					transport.setCredentialsProvider(credentialsProvider);
 
 				final Collection<RemoteRefUpdate> toPush = transport