[BUG] No errors being thrown when accessing empty data from get_driver()

[Carol52x]

Describe the issue:

For the 2018 season and first 6 races of 2019 (could also happen in other seasons i believe, haven't checked though), livetiming api doesn't support keys Reference, CountryCode and HeadshotUrl. When accessing these from session.get_driver(), nothing happens because these keys exist but their values are empty. I think it's beneficial to raise an exception when these are accessed, or have a fallback source to populate these keys instead.

Reproduce the code example:

session = fastf1.get_session(2018, 21, 5)
print(session.get_driver("HAM"))
print(session.get_driver("HAM")['HeadshotUrl'])

Error message:

DriverNumber                              44
BroadcastName                     L HAMILTON
Abbreviation                             HAM
DriverId                            hamilton
TeamName                            Mercedes
TeamColor                             00D2BE
TeamId                              mercedes
FirstName                              Lewis
LastName                            Hamilton
FullName                      Lewis Hamilton
HeadshotUrl
CountryCode
Position                                 1.0
ClassifiedPosition                         1
GridPosition                             1.0
Q1                                       NaT
Q2                                       NaT
Q3                                       NaT
Time                  0 days 01:39:40.382000
Status                              Finished
Points                                  25.0

*No output*