Is your feature request related to a problem? Please describe.
In the ngs_mapping step, the target_coverage_report is always run even for WGS data. In the latter case, there is no description of targets (no path_target_interval_list_mapping), and the sub-step fails.

Describe the solution you'd like
The target_coverage_report should be under user control, with an additional enabled parameter in the model.

Describe alternatives you've considered
The target_coverage_report could be automatically disabled when the bam_collect_doc is enabled. But I think it is not as flexible as putting execution of target_coverage_report directly under user control.
Otherwise, the target_coverage_report enabled parameter default value could be dependent on the type of data (set to False for WGS & RNA, and True to everything else). But again, I think it is unnecessary, and complicates the code. Better wait for a complete re-design of the step.

Additional context
ngs_mapping should really be re-designed