check if value is defined else set to \N
check if value is defined else set to \N

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