switch back to NaN as string

.drone.yml

@@ -10,8 +10,8 @@ platform:
 steps:
 - name: upload
   commands:
-  - service ser2net stop
   - cd gateway
+  - service ser2net stop
   - pio run -e pro-mini
   - echo -n 'reset' > /dev/ttyUSB0; sleep 1s; avrdude -patmega328p -carduino -P/dev/ttyUSB0 -b115200 -D -Uflash:w:.pio/build/pro-mini/firmware.hex:i -v
   - service ser2net start

gateway/src/gateway.cpp

@@ -2,8 +2,6 @@
 #include <RCSwitch.h>
 #include <Adafruit_Sensor.h>
 #include "Tiny.h"
-
-#define ARDUINOJSON_ENABLE_NAN 1
 #include <ArduinoJson.h>
 #include "Dht.h"
 
@@ -50,8 +48,10 @@ bool buildSensorJson(JsonDocument& jsonDoc, unsigned long value) {
 
 	JsonObject sensor = jsonDoc.createNestedObject("sensor");
 
-	unsigned long voltage = GET_VCC(value);
-	sensor["voltage"] = voltage == 0 ? NAN : (float)voltage / 1000;
+	float voltage = (float)GET_VCC(value) / 1000;
+	if (voltage != 0) {
+		sensor["voltage"] = voltage;
+	}
 
 	switch (GET_TYPE(value)) {
 	case SensorType::GENERIC: