streamline of 2d PIV data by Mupad plot::streamlines2d

I have import PIV data x, y, U, V by U:=import::readdata("U.txt",","):, and run plot(plot::Streamlines2d(U,V,x=min(x)..max(x),y=min(y)..max(y),TipLength=3*unit::mm,LineColor=RGB:blue)) I got an error:

[Jianhua LIU]

the error is Expecting an arithmetical expression or function. Got a 'DOM_LIST' for atrribute 'XFunction' in the 'Streamline2d' object.[plot]

please help me work out. Cheers!