<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_output_cwl_keys(fnargs):
 """Retrieve output_cwl_keys from potentially nested input arguments. """

    for d in utils.flatten(fnargs):
        if isinstance(d, dict) and d.get("output_cwl_keys"):
            return d["output_cwl_keys"]
    raise ValueError("Did not find output_cwl_keys in %s" % (pprint.pformat(fnargs)))