Give non null default to L0DUReportMonitor xLabelOptions, required by ROOT 6.24
Fixes the errors
Error in <TH2D::LabelsOption>: is an invalid label placement option!
in the boole.boole-fest test with LCG_100
Edited by Marco Cattaneo
Fixes the errors
Error in <TH2D::LabelsOption>: is an invalid label placement option!
in the boole.boole-fest test with LCG_100