The default behavior of coverage report, coverage html, and coverage xml differs in regards to error handling. If source file is not found, coverage report goes ahead with reporting next sources, coverage html aborts the report creation, resulting in incomplete html directory. Similar behavior with coverage report is achieved when option -i is used.
Also coverage html reports that the source cannot be found, but does not inform the user that the report generation is aborted. Visible message about this, and advise to use -i is an alternative to help the user out of this confusing situation.
See attachments for a testcase to reproduce the situation