Set guid property only if such is registered for given class and datamodel holds value for it. Closes gh-69
Set guid property only if such is registered for given class and
datamodel holds value for it. Closes gh-69

midgardproject/midgard-core,piotras/midgard-core,piotras/midgard-core,midgardproject/midgard-core,midgardproject/midgard-core,piotras/midgard-core,midgardproject/midgard-core,piotras/midgard-core