In the store() method:   When testing for existance of an object xref entry with   linkage_annotation, treat NULLs as equals.
In the store() method:
  When testing for existance of an object xref entry with
  linkage_annotation, treat NULLs as equals.

+ some formatting.

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