circle-radius interpolation on iOS not working anymore

I updated the mapbox plugin from 5.0.0 to 6.2.9 and noticed that the circle-radius interpolation is not working anymore on iOS. Which means that a circle won't be adjusted in size according to the zoom level. The functionality was removed in PR #8

so basically this was removed

const nsDict = new (NSDictionary as any)(stopValues, stopKeys);

const nsArray = NSArray.arrayWithArray([nsDict]);

layer.circleRadius = NSExpression.expressionWithFormatArgumentArray("mgl_interpolate:withCurveType:parameters:stops:( $zoomLevel, 'exponential', 2, %@)", nsArray);

and replaced with a TODO

if (propertiesObject['circle-radius']) {
     if (typeof propertiesObject['circle-radius'] !== 'number') {
         throw new Error('Unsupported circle-radius type'); // TODO: Implement circle radius with stops
     }
     circleProperties['circleRadius'] = NSExpression.expressionForConstantValue(propertiesObject['circle-radius']);
 }

I tried to reintroduce the functionality and created a dictionary with some test values for the NSExpression

const nsDict = new (NSDictionary as any)([0, 5147], [0, 20]);
const nsArray = NSArray.arrayWithArray([nsDict]);
const expression = NSExpression.expressionWithFormatArgumentArray("mgl_interpolate:withCurveType:parameters:stops:( $zoomLevel, 'exponential', 2, %@)", nsArray);

but I get the following error at runtime

MapComponent:addCircle(): addCircle threw an error:Error: Unable to convert JSON object mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, "linear", nil, {0 = 0, 20 = 5147}) to an NSExpression.

Which is weird since the same code was running in the old plugin version. Could it have something to do with the iOS-runtime? My project with the old plugin is running the iOS runtime 6.5.4 where as the new is project is running 8.0.0.

@cvietor did you run into the same issue while refactoring for the above mentioned PR? Might that be the reason you left it as a TODO?

Start at the circle-radius handling in addCircle() and compare the current TODO with the removed implementation from PR #8. Reproduce the stop-based expression on the affected iOS runtime versions; done means circle-radius interpolation works by zoom level without the NSExpression conversion error.