fix lost handler metrics

* since all these classes use a shared FeedContext instance we must make
  sure that nobody ever uses NullFeedMetric (except unit tests & VespaFeeder).

1 files changed, 7 insertions, 0 deletions

diff --git a/vespaclient-core/src/main/java/com/yahoo/feedhandler/NullFeedMetric.java b/vespaclient-core/src/main/java/com/yahoo/feedhandler/NullFeedMetric.java
index b8363ace62d..2940c0fcc44 100644
--- a/vespaclient-core/src/main/java/com/yahoo/feedhandler/NullFeedMetric.java
+++ b/vespaclient-core/src/main/java/com/yahoo/feedhandler/NullFeedMetric.java
@@ -9,6 +9,13 @@ import java.util.Map;
  * @since 5.1.20
  */
 public final class NullFeedMetric implements Metric {
+
+    public NullFeedMetric(boolean flag) {
+        if (!flag) {
+            throw new IllegalArgumentException("must set flag allowing to throw away metrics");
+        }
+    }
+
     @Override
     public void set(String key, Number val, Context ctx) {
     }