api/v3election: error on missing "leader" field

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

etcdserver/api/v3election/election.go

@@ -15,6 +15,8 @@
 package v3election
 
 import (
+	"errors"
+
 	"golang.org/x/net/context"
 
 	"github.com/coreos/etcd/clientv3"
@@ -22,6 +24,10 @@ import (
 	epb "github.com/coreos/etcd/etcdserver/api/v3election/v3electionpb"
 )
 
+// ErrMissingLeaderKey is returned when election API request
+// is missing the "leader" field.
+var ErrMissingLeaderKey = errors.New(`"leader" field must be provided`)
+
 type electionServer struct {
 	c *clientv3.Client
 }
@@ -51,6 +57,9 @@ func (es *electionServer) Campaign(ctx context.Context, req *epb.CampaignRequest
 }
 
 func (es *electionServer) Proclaim(ctx context.Context, req *epb.ProclaimRequest) (*epb.ProclaimResponse, error) {
+	if req.Leader == nil {
+		return nil, ErrMissingLeaderKey
+	}
 	s, err := es.session(ctx, req.Leader.Lease)
 	if err != nil {
 		return nil, err
@@ -98,6 +107,9 @@ func (es *electionServer) Leader(ctx context.Context, req *epb.LeaderRequest) (*
 }
 
 func (es *electionServer) Resign(ctx context.Context, req *epb.ResignRequest) (*epb.ResignResponse, error) {
+	if req.Leader == nil {
+		return nil, ErrMissingLeaderKey
+	}
 	s, err := es.session(ctx, req.Leader.Lease)
 	if err != nil {
 		return nil, err