XDocLoader: Add missing case in switch on DiffMode

Change-Id: Ica5ca38c9d5ef603059df363f01050ed41f1ad02
diff --git a/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocLoader.java b/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocLoader.java
index d98c037..324b0dd 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocLoader.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/xdocs/XDocLoader.java
@@ -252,6 +252,7 @@
       case UNIFIED:
         htmlHeader += "unified.xsl";
         break;
+      case NO_DIFF:
       default:
         log.error(String.format("Unsupported diff mode: %s", diffMode.name()));
         throw new ResourceNotFoundException();