The rest of this constructor was still using the input meshgroup, which might be nullptr. Make it use the field, which was checked for being nullptr and initialised if it was nullptr.
For this I moved the constructor properly to the cpp file. This prevents the constructor from having to be compiled a million times, and having to compile a million other files each time you modify this constructor, and prevents having to compile the FffProcessor header each time too. Also, since meshgroup must be defined before initializeRetractionConfigs and initializeSkirtConfigs, they are now in the body of the constructor to properly define the order.
Tim Kuipers