[Fix] metric_exporter: avoid sending `nil` in metric values

diff --git a/src/plugins/lua/metric_exporter.lua b/src/plugins/lua/metric_exporter.lua
index 75885516c3304d74cfd605d513f79aa5ec9ca505..3de87c157a29a3eee774d99fc087d7d4d36153bc 100644 (file)
--- a/src/plugins/lua/metric_exporter.lua
+++ b/src/plugins/lua/metric_exporter.lua
@@ -117,7 +117,7 @@ local function graphite_push(kwargs)
     elseif #split == 2 then
       mvalue = kwargs['stats'][split[1]][split[2]]
     end
-    table.insert(metrics_str, string.format('%s %s %s', mname, mvalue, stamp))
+    table.insert(metrics_str, string.format('%s %s %s', mname, mvalue or 'null', stamp))
   end
 
   metrics_str = table.concat(metrics_str, '\n')