enforce video.size_id for video imps in rubicon adapter

adapters/rubicon/rubicon.go

@@ -5,13 +5,14 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"github.com/golang/glog"
-	"github.com/prebid/prebid-server/pbs"
 	"io/ioutil"
 	"net/http"
 	"net/url"
 	"strings"
 
+	"github.com/golang/glog"
+	"github.com/prebid/prebid-server/pbs"
+
 	"golang.org/x/net/context/ctxhttp"
 
 	"github.com/mxmCherry/openrtb"
@@ -683,6 +684,13 @@ func (a *RubiconAdapter) MakeRequests(request *openrtb.BidRequest, reqInfo *adap
 
 		isVideo := isVideo(thisImp)
 		if isVideo {
+			if rubiconExt.Video.VideoSizeID == 0 {
+				errs = append(errs, &errortypes.BadInput{
+					Message: fmt.Sprintf("imp[...].ext.bidder.rubicon.video.size_id must be defined for video impression #%d", i),
+				})
+				continue
+			}
+
 			videoCopy := *thisImp.Video
 			videoExt := rubiconVideoExt{Skip: rubiconExt.Video.Skip, SkipDelay: rubiconExt.Video.SkipDelay, RP: rubiconVideoExtRP{SizeID: rubiconExt.Video.VideoSizeID}}
 			videoCopy.Ext, err = json.Marshal(&videoExt)

adapters/rubicon/rubicontest/supplemental/required-video-size-id.json

@@ -0,0 +1,31 @@
+{
+    "mockBidRequest": {
+        "id": "test-req-id",
+        "imp": [
+            {
+                "id": "test-imp-1",
+                "video": {
+                    "w": 640,
+                    "h": 480,
+                    "linearity": 1
+                },
+                "ext": {
+                    "bidder": {
+                        "accountId": 1001,
+                        "siteId":113932,
+                        "zoneId":535510
+                    }
+                }
+            }
+        ],
+        "site": {
+            "page": "prebid.org"
+        }
+    },
+    "expectedMakeRequestsErrors": [
+        {
+            "value": "imp[...].ext.bidder.rubicon.video.size_id must be defined for video impression #0",
+            "comparison": "literal"
+        }
+    ]
+}