getSectionIDNum may return same value for two different MBBSectionID.
e.g. A Cold type MBBSectionID with number 0 and a Default type
MBBSectionID with number 2 get same value 2 from getSectionIDNum. This
may lead to overwrite of MBBSectionRanges. Using MBBSectionID itself
as DenseMap key is better choice.