ran go mod vendor on the whole project

vendor/github.com/gogo/protobuf/proto/encode.go

@@ -37,9 +37,27 @@ package proto
 
 import (
 	"errors"
+	"fmt"
 	"reflect"
 )
 
+// RequiredNotSetError is the error returned if Marshal is called with
+// a protocol buffer struct whose required fields have not
+// all been initialized. It is also the error returned if Unmarshal is
+// called with an encoded protocol buffer that does not include all the
+// required fields.
+//
+// When printed, RequiredNotSetError reports the first unset required field in a
+// message. If the field cannot be precisely determined, it is reported as
+// "{Unknown}".
+type RequiredNotSetError struct {
+	field string
+}
+
+func (e *RequiredNotSetError) Error() string {
+	return fmt.Sprintf("proto: required field %q not set", e.field)
+}
+
 var (
 	// errRepeatedHasNil is the error returned if Marshal is called with
 	// a struct with a repeated field containing a nil element.