Fix NPE when username or password isn't specified for remote

When the username or password is not specified, pass an empty
string instead of null.

Change-Id: I49121b9873eb9f2800417b6d264cc2ad82047f85

src/main/java/com/googlesource/gerrit/plugins/replication/SecureCredentialsFactory.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/SecureCredentialsFactory.java b/src/main/java/com/googlesource/gerrit/plugins/replication/SecureCredentialsFactory.java
index 2b0c16b..c518091 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/SecureCredentialsFactory.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/SecureCredentialsFactory.java
@@ -17,6 +17,7 @@
 import com.google.gerrit.server.config.SitePaths;
 import com.google.inject.Inject;
 import java.io.IOException;
+import java.util.Objects;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
@@ -49,8 +50,8 @@
 
   @Override
   public SecureCredentialsProvider create(String remoteName) {
-    String user = config.getString("remote", remoteName, "username");
-    String pass = config.getString("remote", remoteName, "password");
+    String user = Objects.toString(config.getString("remote", remoteName, "username"), "");
+    String pass = Objects.toString(config.getString("remote", remoteName, "password"), "");
     return new SecureCredentialsProvider(user, pass);
   }
 }