How to programatically remove NSValueTransformer Binding

I'm binding a value transformer like this:

optionsDict = [NSBindingOption.valueTransformer:decToHexTransformer(), NSBindingOption.valueTransformerName:NSValueTransformerName.decToHexTransformerName]
plcAddrLabel.bind(.value, to: self, withKeyPath: "plcRegisterAddress" , options: optionsDict)

To remove the transformer I have tried this:

plcAddrLabel.unbind(.value)
plcAddrLabel.bind(.value, to: self, withKeyPath: "plcRegisterAddress" , options: nil)

but the transformer is still present after the bind operation, it appears unbind doesn't remove it.

and I tried this:

optionsDict = [NSBindingOption.valueTransformer: "<null>", NSBindingOption.valueTransformerName: "<null>"]
plcAddrLabel.bind(.value, to: self, withKeyPath: "plcRegisterAddress" , options: optionsDict)

which immediately triggers the error -[NSTaggedPointerString transformedValue:]: unrecognized selector sent to instance upon execution of the bind function.

same error is caused with this code:

optionsDict = [NSBindingOption.valueTransformer: NSBindingOption.nullPlaceholder, NSBindingOption.valueTransformerName: NSBindingOption.nullPlaceholder]

Is there a way to programatically remove a transformer from a binding?