Protect against null pointer for BaseCommand

Subclasses of BaseCommand may not initialize argv field (e.g.
ScpCommand).
Recent change [1] uses argv field which may result in NPE.

This change will guard the code from such error.

[1]: https://gerrit-review.googlesource.com/c/gerrit/+/146191

Change-Id: I6dd3afa08fd696d25741b5bdec8530deac422261
Signed-off-by: Ardo Septama <aseptama@gmail.com>

gerrit-sshd/src/main/java/com/google/gerrit/sshd/BaseCommand.java

@@ -414,6 +414,9 @@ public abstract class BaseCommand implements Command {
   }
 
   private void maskSensitiveParameters() {
+    if (argv == null) {
+      return;
+    }
     sensitiveParameters = cache.get(this.getClass());
     maskedArgv = new ArrayList<>();
     maskedArgv.add(commandName);