diff --git a/core-telemetry.cabal b/core-telemetry.cabal
--- a/core-telemetry.cabal
+++ b/core-telemetry.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           core-telemetry
-version:        0.2.2.0
+version:        0.2.3.0
 synopsis:       Advanced telemetry
 description:    This is part of a library to help build command-line programs, both tools and
                 longer-running daemons.
diff --git a/lib/Core/Telemetry/Observability.hs b/lib/Core/Telemetry/Observability.hs
--- a/lib/Core/Telemetry/Observability.hs
+++ b/lib/Core/Telemetry/Observability.hs
@@ -267,6 +267,9 @@
 instance Telemetry String where
     metric k v = MetricValue (JsonKey k) (JsonString (intoRope v))
 
+instance Telemetry () where
+    metric k _ = MetricValue (JsonKey k) JsonNull
+
 {- |
 The usual warning about assuming the @ByteString@ is ASCII or UTF-8 applies
 here. Don't use this to send binary mush.