Numbers in JSON result in reboot
```
␛[0;32mI (70039) MQTT: MQTT_EVENT_DATA␛[0m
assertion "IsString()" failed: file "/Users/sierenmusic/Development/HomeControl/main/libraries/rapidjson/include/rapidjson/document.h", line 1773, function: const Ch* rapidjson::GenericValue<Encoding, Allocator>::GetString() const [with Encoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>; rapidjson::GenericValue<Encoding, Allocator>::Ch = char]
abort() was called at PC 0x40189b03 on core 0

ELF file SHA256: 18faed4d03d75adc

Backtrace: 0x4008685c:0x3ffd2460 0x40086c35:0x3ffd2480 0x40189b03:0x3ffd24a0 0x400ddaa0:0x3ffd24d0 0x400e008f:0x3ffd24f0 0x400e016d:0x3ffd2690 0x400e0279:0x3ffd2720 0x400e02f7:0x3ffd2790 0x400dda7d:0x3ffd27c0 0x400ddc51:0x3ffd27f0 0x400ddc89:0x3ffd2810 0x4011a1ea:0x3ffd2830 0x4011aac8:0x3ffd2850

Rebooting...
```

config:
```json
    "name": "Temperatur b",
    "type": "Sensor",
    "icon": "door",
    "devices": [{
      "name": "Temp b",
      "type": "singleValue",
      "jsondata": true,
      "firstIcon": "temperature_small",
      "firstKey": "val",
      "getTopic": "hm/status/Wandthermostat:2/ACTUAL_TEMPERATURE"
    },
```

mqtt-payload:
```json
{
  "val":3.1,
   "ts":1608319032692,
  "lc":1608306604934
}
```