Making a chart in native resolution

When I use “ui.Chart.image.seriesByRegion” command in Google Earth Engine it required to define the spatial scale of the raster. Please, look at the below command, if I remove “250” it shows error. I did a search, but could not find clear solution for it.

I have tried to apply the solution given in Exporting images in native CRS and resolution, but it did not work as well “NDVI.projection is not a function”.

Is there any possibility to keep native spatial scale of the image while producing chart?

var pts = ee.Geometry.Point([10.61134244284358, 50.00619843404531]);

var NDVI = ee.ImageCollection("MODIS/006/MOD13A1")
    .select(['NDVI'])
    .filterDate('2018-01-01', '2019-06-25');

print(NDVI);

var chart = ui.Chart.image.seriesByRegion(NDVI, pts, ee.Reducer.first(), 'NDVI', 250)
.setChartType('LineChart');

print(chart);