Transform / Scale Roller Shutter Dimmer Value


I’m using a Fibaro FGR222 Roller Shutter 2 for blinds.
They have a channel called “shutter position” and is of type “dimmer”.
So far so good.
When I display the value in Habpanel, it shows the position of the blinds between 0 and 100.

Dimmer FF_Blinds_Ruben {channel="zwave:device:3d4427ff:node7:blinds_shutter" }

and in habpanel simple:

Value of DIMMER (Ruben) is: {{itemValue('FF_Blinds_Ruben')}}

This all works and buttons with ng-click also work:

<button class="blinds"><span class="blindsCenter" ng-click="sendCmd('FF_Blinds_Ruben', '50')">50</span></button>

The blinds are going to 50% and the itemValue is displayed correctly.

Now here’s the problem. I would like to have the itemValue scaled so I can use the scaled value for displaying the correct icon.
However, when I create an item:

Number blindsValueScaled "Scaled Dimmer: [SCALE(blinds.scale):%s]" {channel="zwave:device:3d4427ff:node7:blinds_shutter" }

This item has NULL and does not change.
The logfile show:

14-Nov-2019 19:03:46.564 [WARN ] [e.core.transform.AbstractFileTransformationService] - Could not transform 'NULL' with the file 'blinds.scale' : Scale must be used with numeric inputs, valid quantity types or a 'NaN' entry.

The strange thing is that I use exactly the same transformation for my Fibaro dimmers. Which also has this type “dimmer” and that works like a charm.

Anyone an idea of what I’m doing wrong. It’s probably the “dimmer” type which is not a number? but in that case, how could I do the transformation?

Thanks in advance!