code: def _check_hetcaller(item):
      
      svs = _get_as_list(item, "svcaller")
      hets = _get_as_list(item, "hetcaller")
      if hets or any([x in svs for x in ["titancna", "purecn"]]):
          if not any([x in svs for x in ["cnvkit", "gatk-cnv"]]):
              raise ValueError("Heterogeneity caller used but need CNV calls. Add `gatk4-cnv` "
                               "or `cnvkit` to `svcaller` in sample: %s" % item["description"])
docs: Ensure upstream SV callers requires to heterogeneity analysis are available.