feat(core): DateTime and StatusCode are nullable in the JSON encoding
feat(core): DateTime and StatusCode are nullable in the JSON encoding

JGrothoff/open62541,jpfr/open62541,open62541/open62541,open62541/open62541,JGrothoff/open62541,jpfr/open62541,JGrothoff/open62541,jpfr/open62541,JGrothoff/open62541,open62541/open62541,open62541/open62541,jpfr/open62541