<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_path_exists(s):
 """If s is a path, return s, else False"""

    if s is None:
        return None
    if os.path.exists(s):
        return s
    else:
        raise ValueError('"%s" should be a path but it does not exist' % s)