isOptional       1138 third_party/protobuf/java/src/main/java/com/google/protobuf/Descriptors.java           if (!isOptional() || getType() != Type.MESSAGE) {
isOptional        234 third_party/protobuf/java/src/main/java/com/google/protobuf/ExtensionRegistry.java         field.isOptional() &&
isOptional        299 third_party/protobuf/java/src/main/java/com/google/protobuf/TextFormat.java             && (field.isOptional())