return nil if resource model type is not known
return nil if resource model type is not known

OpenBEL/openbel-server,OpenBEL/openbel-api,nbargnesi/openbel-server,OpenBEL/openbel-api,nbargnesi/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-api,OpenBEL/openbel-server,OpenBEL/openbel-server,nbargnesi/openbel-server