fix bug in SourcesContextMixin
fix bug in SourcesContextMixin

PersonalGenomesOrg/open-humans,OpenHumans/open-humans,OpenHumans/open-humans,OpenHumans/open-humans,PersonalGenomesOrg/open-humans,PersonalGenomesOrg/open-humans,OpenHumans/open-humans,PersonalGenomesOrg/open-humans