def field_names_to_request(self, conform):
        if not conform:
            return None

        fields = set()
        for k, v in conform.items():
            if k in attrib_types:
                if isinstance(v, dict):
                    # It's a function of some sort
                    fields.add(v.get('field'))
                elif isinstance(v, list):
                    # It's a list of field names
                    for f in v:
                        fields.add(f)
                else:
                    fields.add(v)

        if fields:
            return list(filter(None, sorted(fields)))
        else:
            return None
Return list of fieldnames to request based on conform, or None.
dataset/ETHPy150Open openaddresses/machine/openaddr/cache.py/EsriRestDownloadTask.field_names_to_request