As per https://confluence.atlassian.com/display/CLOVER/%27Current%27+Report, Clover is unable to count NCLOC (non-commented lines of code) for Groovy code.

Because of this limitation, if project contains Groovy code only, the 'Lines of code' chart always shows zero. Clover can display LOC value for Groovy language, however.

Therefor, we could draw both NCLOC and LOC lines on a chart.