fix a ui regression introduced by sha bb4d76
fix a ui regression introduced by sha bb4d76

SHA bb4d76 caused nil to be passed to type_of_sequences for empty
sequence, causing it to raise a NoMethodError, causing the AJAX request
(to determine the sequence type) to fail.

elsiklab/sequenceserver,yeban/sequenceserver,aldermossy/sequenceserver,jasminZ/sequenceserver,yeban/sequenceserver,deepakunni3/sequenceserver,IsmailM/sequenceserver,vivekiitkgp/sequenceserver,jasminZ/sequenceserver,elsiklab/sequenceserver,IsmailM/sequenceserver,IsmailM/sequenceserver,vivekiitkgp/sequenceserver,elsiklab/sequenceserver,aldermossy/sequenceserver,lepbase/lepbase-sequenceserver,deepakunni3/sequenceserver,jasminZ/sequenceserver,aldermossy/sequenceserver,vivekiitkgp/sequenceserver,aldermossy/sequenceserver,lepbase/lepbase-sequenceserver,yeban/sequenceserver,yeban/sequenceserver,deepakunni3/sequenceserver,lepbase/lepbase-sequenceserver