made attrib_type.description optional
made attrib_type.description optional

muffato/ensembl,mjg17/ensembl,at7/ensembl,james-monkeyshines/ensembl,willmclaren/ensembl,james-monkeyshines/ensembl,mjg17/ensembl,Ensembl/ensembl,james-monkeyshines/ensembl,muffato/ensembl,at7/ensembl,danstaines/ensembl,muffato/ensembl,muffato/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl,willmclaren/ensembl,danstaines/ensembl,at7/ensembl,Ensembl/ensembl,Ensembl/ensembl,mjg17/ensembl,mjg17/ensembl,at7/ensembl,danstaines/ensembl