- fixed an 'null' issue in Study domain
- fixed an 'null' issue in Study domain

PhenotypeFoundation/PhenotypeDatabase-legacy,thehyve/GSCF,PhenotypeFoundation/PhenotypeDatabase-legacy,PhenotypeFoundation/PhenotypeDatabase,NetherlandsMetabolomicsCentre/GSCF,TNO/PhenotypeDatabase,TNO/PhenotypeDatabase,PhenotypeFoundation/PhenotypeDatabase-legacy,NetherlandsMetabolomicsCentre/GSCF,PhenotypeFoundation/PhenotypeDatabase,thehyve/GSCF