Background Field presence is the notion of whether a protobuf field has a value. There are two different manifestations of presence for protobufs: no presence, where the generated message API stores field values (only), and explicit presence, where the API also stores whether or not a field has been set. Historically, proto2 has mostly followed explicit presence, while proto3 exposes only no presence semantics. Singular proto3 fields of basic types (numeric, string, bytes, and enums) which ar...
