Trying to build package in ROS melodic

[PhilipAmadasun]

I'm trying to build the ROS melodic branch. I get this error:

Errors     << multirobot_map_merge:make /home/philip/catkin_ws/logs/multirobot_map_merge/build.make.000.log
In file included from /home/philip/catkin_ws/src/m-explore/map_merge/src/combine_grids/merging_pipeline.cpp:46:0:
/home/philip/catkin_ws/src/m-explore/map_merge/src/combine_grids/estimation_internal.h: In function ‘cv::Ptr<cv::Feature2D> combine_grids::internal::chooseFeatureFinder(combine_grids::FeatureType)’:
/home/philip/catkin_ws/src/m-explore/map_merge/src/combine_grids/estimation_internal.h:68:14: error: ‘xfeatures2d’ has not been declared
       return xfeatures2d::SURF::create();

What dependency am I missing?