def _check_svcaller(item):
    """Ensure the provide structural variant caller is valid.
    """
    allowed = set(reduce(operator.add, [list(d.keys()) for d in structural._CALLERS.values()]) + [None, False])
    svs = item["algorithm"].get("svcaller")
    if not isinstance(svs, (list, tuple)):
        svs = [svs]
    problem = [x for x in svs if x not in allowed]
    if len(problem) > 0:
        raise ValueError("Unexpected algorithm 'svcaller' parameters: %s\n"
                         "Supported options: %s\n" % (" ".join(["'%s'" % x for x in problem]),
                                                      sorted(list(allowed))))
Ensure the provide structural variant caller is valid.