pg_stats avg_width and null_frac

Can anyone confirm that the "avg_width" reported in the pg_stats is the
avg_width not including any null rows?

ie if a field had:

avg_width: 6
null_frac: 0.5

Then
- 50% of the rows would be empty for this field
- The other 50% of the rows would have data with an avg_width of 6 bytes?
(according to the sampled data at least)

Paul