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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _variant_hla(checkpoints):
 """Add hla analysis to workflow, if configured. """

    if not checkpoints.get("hla"):
        return [], []
    hla = [s("hla_to_rec", "multi-batch",
             [["hla", "fastq"],
              ["config", "algorithm", "hlacaller"]],
               [cwlout("hla_rec", "record")],
               "bcbio-vc", cores=1, no_files=True),
           s("call_hla", "multi-parallel",
             [["hla_rec"]],
             [cwlout(["hla", "hlacaller"], ["string", "null"]),
              cwlout(["hla", "call_file"], ["File", "null"])],
             "bcbio-vc", ["optitype;env=python2", "razers3=3.5.0", "coincbc"])]
    return hla, [["hla", "call_file"]]