code: def _check_jointcaller(data):
      
      allowed = set(joint.get_callers() + [None, False])
      cs = data["algorithm"].get("jointcaller", [])
      if not isinstance(cs, (tuple, list)):
          cs = [cs]
      problem = [x for x in cs if x not in allowed]
      if len(problem) > 0:
          raise ValueError("Unexpected algorithm 'jointcaller' parameter: %s\n"
                           "Supported options: %s\n" % (problem, sorted(list(allowed), key=lambda x: x or "")))
docs: Ensure specified jointcaller is valid.