Grouped barchart not grouping datasets with AndroidChart

First of all english isn't my first language so please excuse errors. I'm using Android Studio, some years ago i wrote a simple app to store some data and generate different graphs (not in real time), it was in java and using MPAndroidChart. Now i wanted to update the app and i decided to convert to kotlin (it wasn't so difficult) and i wanted to update the graph library too, so after trying some others i used AndroidChart (a fork of MPAndroidChart), but now grouping of datasets doesn't work (single dataset, and stacked datasets are ok).

This is the reduced code to an only one function:

private fun testbargroup(): BarData {
        var titolo = "dataset 1"
        var titolo2 = "dataset 2"
        val set1: BarDataSet
        var set2: BarDataSet
        val serie1: ArrayList<BarEntry> = arrayListOf<BarEntry>()
        var serie2: ArrayList<BarEntry> = arrayListOf<BarEntry>()

        for (i in 0..12) {
            serie1.add(BarEntry(i.toFloat(), ((i*0.8)+1).toFloat()))
            serie2.add(BarEntry(i.toFloat(), ((i*1.2)+0.9).toFloat()))
        }

        set1 = BarDataSet(serie1, titolo) //perchè serve anche per il mensile
        set1.setDrawValues(true)
        set1.color = getColor(R.color.colorSet1)
        set1.setValueTextColor(R.color.colorSet1)
        set2 = BarDataSet(serie2, titolo2)
        set2.setDrawValues(true)
        set2.color = getColor(R.color.colorSet2)
        set2.setValueTextColor(R.color.colorSet2)
        val dataSets: ArrayList<IBarDataSet> = ArrayList()
        dataSets.add(set1)
        dataSets.add(set2!!)
        var bdata = BarData(dataSets)
        mChart.setData(bdata)
        mChart.barData.setValueFormatter(CustDefValueFormatter())
        val xAxis = mChart.xAxis
        xAxis.textColor = getColor(R.color.colorDark1)
        mChart.setFitBars(true)
        //dimension istandard per 1 set di barre
        bdata.barWidth = 0.9f
        bdata.setValueTextSize(9f)
        mChart.xAxis.setCenterAxisLabels(false)
        if (bdata.getDataSetCount() == 2) { //se ci sono più datasets (noi al max 2) raggruppiamo, altrimenti sovrappone
            mChart.xAxis.setCenterAxisLabels(true)
            val groupSpace = 0.2f
            val barSpace = 0.0f
            val barWidth = 0.4f
            mChart.groupBars(1f, groupSpace, barSpace)
            bdata.barWidth = barWidth
            bdata.setValueTextSize(6f)
        }
        mChart.invalidate()
        return bdata
    }

mChart initiated in onCreate with findviewbyid, xml layout file is the same in both versions

And here the result, with bars not grouped: Graph

Thanks in advance for any suggestion (I know that the code can be improved, first af all let it works as expected!)

I found the solution, in case of multiple datasets i don't have to set barWidth property.