Consider a read where the base qualities are not stored, we could:

1. Except, with a better message than we currently have (I believe we'll get an index out of bounds exception).
2. Add an option to the consensus callers to use a default base quality when base qualities are missing (e.g. Q30).
3. Add an option to the consensus callers where we can provide a default base quality when base qualities are missing (e.g. Q30). By default it is None, so base qualities are required, but used only when explicitly specified.
4. Others?

The issue with (1) is that would force folks to filter out such reads if they want to get the consensus caller to work. The issue with (2 )is that someone produces a BAM file accidentally with missing qualities and fgbio handles it gracefully, and they would have preferred to have known about it (no one reads the logs).