<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def pid_exists(value, pidtype=None):
 """Check if a persistent identifier exists. :param value: The PID value. :param pidtype: The pid value (Default: None). :returns: `True` if the PID exists. """

    try:
        PersistentIdentifier.get(pidtype, value)
        return True
    except PIDDoesNotExistError:
        return False