asp.net mvc - ?: and ?? Operators with Entity Framework -

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why these operators not work within these examples?

person.cityname = personinfo.cities.cityname ?? "-";

or

person.cityname = personinfo.cities.cityname == null ? "-" : personinfo.cities.cityname;

view generates system.nullreferenceexception. if not allowed advice?

if cityname column nullable, should check hasvalue property follows. , if like, can check if either personinfo or personinfo.cities null. 

person.cityname = personinfo != null                    && personinfo.cities != null                    && personinfo.cities.cityname.hasvalue                    ? personinfo.cities.cityname.value : "-";

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