@staticmethod<EOL><INDENT>def _set_default_key(mapping):<DEDENT>
key_longest = sorted([(len(v), k) for k, v in mapping.items()],<EOL>reverse=True)[<NUM_LIT:0>][<NUM_LIT:1>]<EOL>mapping['<STR_LIT:default>'] = key_longest<EOL>del (mapping[key_longest])<EOL>
Replace the field with the most features with a 'default' field.