RESTWS-306: POST to /obs with value in the beginning throws error

Tests in error: 
shouldRenderHydratedAttributable(org.openmrs.module.webservices.rest.web.v1_0.controller.openmrs1_8.PersonAttributeController1_8Test): hydratedObject on class org.openmrs.PersonAttribute
shouldAddConceptAttributeToPerson(org.openmrs.module.webservices.rest.web.v1_0.controller.openmrs1_8.PersonAttributeController1_8Test): hydratedObject on class org.openmrs.PersonAttribute

Tests in error: 
shouldAddAnAttributeToAVisit(org.openmrs.module.webservices.rest.web.v1_0.controller.openmrs1_9.VisitAttributeController1_9Test): value on class org.openmrs.VisitAttribute
shouldAddAttributeToLocation(org.openmrs.module.webservices.rest.web.v1_0.controller.openmrs1_9.LocationAttributeController1_9Test): value on class org.openmrs.LocationAttribute
shouldAddAttributeToProvider(org.openmrs.module.webservices.rest.web.v1_0.controller.openmrs1_9.ProviderAttributeController1_9Test): value on class org.openmrs.ProviderAttribute