New MQTT Binding does not work, although other topics are fine

Today I added a illuminance sensor that publishes its values using mqtt.
The values are positive integers without any dot or comma.
The message size for a single digit value is 2 bytes (value + null termination).
The topic is “flur/illuminance”.
I used copy & paste to make sure openHAB has the correct topic.
This is working and verified using mqtt-spy.
However the item in openHAB does not get updated although the mqtt topic receives new messages, its state is always “null”.

This is my Item:

Number Flur_Illuminance "Flur Beleuchtungsstärke [%.2f Lux]" <illuminance> { mqtt="<[mqttBroker:flur/illuminance:state:default]" }

I have other items configured using mqtt which are working fine, like these:

Number Wohnzimmer_Temperature "Wohnzimmer Temperatur [%.2f °C]" <temperature> (Wohnzimmer_Heizung) [ "CurrentTemperature" ] { mqtt="<[mqttBroker:wohnzimmer/temperature:state:default]" }

Switch Flur_Presence "Flur Präsenzmelder" {mqtt="<[mqttBroker:flur/presence:state:default]"}

Does your log show any errors?

Neither openhab.log, nor events.log have any entries regarding this item besides a couple entries like this:

2018-04-08 23:05:28.339 [ome.event.ItemUpdatedEvent] - Item 'Flur_Illuminance' has been updated.

Odd, I don’t see anything wrong if your item definition.
Try copying and pasting a working mqtt item, change the name to testItem and change the topic to flur/illuminance
Save the item file
Send a value on that topic from mqttfx, what happens?

Thanks for your help, I found the error in my arduino program when I copied the topic to publish a message to it by hand:

const char* topicLux = "flur/illuminance ";

There was a whitespace at the end of the topic.

Cool, well done, good bit of debugging!
Beware of copy and paste!
Please mark the thread as solved, thanks