Fix broken AdAdaptor NPE on init

when per-server password is not specified

src/com/google/enterprise/adaptor/ad/AdAdaptor.java

diff --git a/src/com/google/enterprise/adaptor/ad/AdAdaptor.java b/src/com/google/enterprise/adaptor/ad/AdAdaptor.java
index 0a0c899..70ba0e0 100644
--- a/src/com/google/enterprise/adaptor/ad/AdAdaptor.java
+++ b/src/com/google/enterprise/adaptor/ad/AdAdaptor.java
@@ -122,10 +122,11 @@
       if (principal.isEmpty()) {
         throw new IllegalStateException("user not specified for host " + host);
       }
-      String passwd = context.getSensitiveValueDecoder().decodeValue(
-          singleServerConfig.get("password"));
+      String passwd = singleServerConfig.get("password");
       if (null == passwd) {
         passwd = defaultPassword;
+      } else {
+        passwd = context.getSensitiveValueDecoder().decodeValue(passwd);
       }
       if (passwd.isEmpty()) {
         throw new IllegalStateException("password not specified for host "