Variable label_types is not defined in function check_read_inputs in file wfdb/io/annotation.py #253
Description
I was using wfdb library, I passed the wrong argument return_label_elements=['qrs'] to the function wfdb.rdann, and I got a NameError instead of the expected exception that is thrown when an invalid value for return_label_elements is passed.
Instead of catenating label_types to the error message, you must catenate ann_label_fields.
https://github.com/MIT-LCP/wfdb-python/blob/master/wfdb/io/annotation.py#L1717
