AlignRecords doesn't handle missing data

[Jason Vander Heiden]

AlignRecords-block (and presumably all commands) don’t handle cases with missing data in the sequence columns. Empty sequence records aren’t multiple aligned by muscle, so a key error is returned when trying to retrieve the muscle results.

Records with empty strings for sequence data should be failed before being passed to muscle.

[Jason Vander Heiden]

Fixed in 21bfbe3.