Rust concept piecemeal summary

There is no concept of 1.Rust null, but in fact there are many places that need the concept of a null, this time we can use Option instead, it is a generic wrapper class T, that is, in the C # int? Or Java, the Optional;

[But deserialization seemingly is not null concept, without this attribute with the default value like, Java's Json deserialization itself is seemingly doing]