Classification problem (nullpointerexception)

Hi guys. i am new on snap program and i am trying to make a unsupervised classification via Sentinel 2 satellite images. But when i choose the unsupervised classification i am getting this error. Anyone know why am i getting this?

have you reprojected your data to WGS84 before classification?
At the moment, classification only works with reprojected data - you find more information on this here:

yes it worked! thank you sir for reply.

i want to ask one more thing, can i do accurracy analysis in SNAP?

currently, this is not included, but you can use the pin manager to extract pixel values at selected points for external use.

hi can u please tell me how u did the reprojection . how do fill the coordinate systeme