check if there are no fields (only tags), in which case add an integer field "n" with value 1

src/influx.rs

@@ -354,6 +354,10 @@ impl InfluxWriter {
 
                         if meas.timestamp.is_none() { meas.timestamp = Some(now()) }
 
+                        if meas.fields.is_empty() {
+                            meas.fields.push(("n", OwnedValue::Integer(1)));
+                        }
+
                         //#[cfg(feature = "trace")] { if count % 10 == 0 { trace!(logger, "rcvd new measurement"; "count" => count, "key" => meas.key); } }
 
                         count = next(count, &meas, &mut buf, &loop_time, &mut last);