The Code Change Report generation may fail if a new file is added in the src directory and that file contains functions for which Metrix++ generates complexity data.

The expected behaviour is that newly added source files work correctly. 

The actual behaviour is that the code_change_info.py does not check that the previous complexity data contains information on a particular file before attempting to access it in the preprocessed_prev_complexity_data dictionary. The issue was found during work on a PR for WT-12619.
 
This ticket will fix the issue.