diff --git a/cdp/animation/easyjson.go b/cdp/animation/easyjson.go
index c052fa0..8d1ac35 100644
--- a/cdp/animation/easyjson.go
+++ b/cdp/animation/easyjson.go
@@ -1464,12 +1464,14 @@ func easyjsonC5a4559bEncodeGithubComKnqChromedpCdpAnimation17(out *jwriter.Write
 	first = false
 	out.RawString("\"fill\":")
 	out.String(string(in.Fill))
-	if !first {
-		out.RawByte(',')
+	if in.BackendNodeID != 0 {
+		if !first {
+			out.RawByte(',')
+		}
+		first = false
+		out.RawString("\"backendNodeId\":")
+		out.Int64(int64(in.BackendNodeID))
 	}
-	first = false
-	out.RawString("\"backendNodeId\":")
-	out.Int64(int64(in.BackendNodeID))
 	if in.KeyframesRule != nil {
 		if !first {
 			out.RawByte(',')
@@ -1606,6 +1608,8 @@ func easyjsonC5a4559bDecodeGithubComKnqChromedpCdpAnimation19(in *jlexer.Lexer,
 			out.StartTime = float64(in.Float64())
 		case "currentTime":
 			out.CurrentTime = float64(in.Float64())
+		case "type":
+			(out.Type).UnmarshalEasyJSON(in)
 		case "source":
 			if in.IsNull() {
 				in.Skip()
@@ -1616,8 +1620,6 @@ func easyjsonC5a4559bDecodeGithubComKnqChromedpCdpAnimation19(in *jlexer.Lexer,
 				}
 				(*out.Source).UnmarshalEasyJSON(in)
 			}
-		case "type":
-			(out.Type).UnmarshalEasyJSON(in)
 		case "cssId":
 			out.CSSID = string(in.String())
 		default:
@@ -1680,18 +1682,20 @@ func easyjsonC5a4559bEncodeGithubComKnqChromedpCdpAnimation19(out *jwriter.Write
 		out.RawByte(',')
 	}
 	first = false
-	out.RawString("\"source\":")
-	if in.Source == nil {
-		out.RawString("null")
-	} else {
-		(*in.Source).MarshalEasyJSON(out)
-	}
-	if !first {
-		out.RawByte(',')
-	}
-	first = false
 	out.RawString("\"type\":")
 	(in.Type).MarshalEasyJSON(out)
+	if in.Source != nil {
+		if !first {
+			out.RawByte(',')
+		}
+		first = false
+		out.RawString("\"source\":")
+		if in.Source == nil {
+			out.RawString("null")
+		} else {
+			(*in.Source).MarshalEasyJSON(out)
+		}
+	}
 	if in.CSSID != "" {
 		if !first {
 			out.RawByte(',')
diff --git a/cdp/animation/types.go b/cdp/animation/types.go
index cd4f7df..facd34c 100644
--- a/cdp/animation/types.go
+++ b/cdp/animation/types.go
@@ -13,16 +13,16 @@ import (
 
 // Animation animation instance.
 type Animation struct {
-	ID           string  `json:"id"`              // Animation's id.
-	Name         string  `json:"name"`            // Animation's name.
-	PausedState  bool    `json:"pausedState"`     // Animation's internal paused state.
-	PlayState    string  `json:"playState"`       // Animation's play state.
-	PlaybackRate float64 `json:"playbackRate"`    // Animation's playback rate.
-	StartTime    float64 `json:"startTime"`       // Animation's start time.
-	CurrentTime  float64 `json:"currentTime"`     // Animation's current time.
-	Source       *Effect `json:"source"`          // Animation's source animation node.
-	Type         Type    `json:"type"`            // Animation type of Animation.
-	CSSID        string  `json:"cssId,omitempty"` // A unique ID for Animation representing the sources that triggered this CSS animation/transition.
+	ID           string  `json:"id"`               // Animation's id.
+	Name         string  `json:"name"`             // Animation's name.
+	PausedState  bool    `json:"pausedState"`      // Animation's internal paused state.
+	PlayState    string  `json:"playState"`        // Animation's play state.
+	PlaybackRate float64 `json:"playbackRate"`     // Animation's playback rate.
+	StartTime    float64 `json:"startTime"`        // Animation's start time.
+	CurrentTime  float64 `json:"currentTime"`      // Animation's current time.
+	Type         Type    `json:"type"`             // Animation type of Animation.
+	Source       *Effect `json:"source,omitempty"` // Animation's source animation node.
+	CSSID        string  `json:"cssId,omitempty"`  // A unique ID for Animation representing the sources that triggered this CSS animation/transition.
 }
 
 // Effect animationEffect instance.
@@ -34,7 +34,7 @@ type Effect struct {
 	Duration       float64           `json:"duration"`                // AnimationEffect's iteration duration.
 	Direction      string            `json:"direction"`               // AnimationEffect's playback direction.
 	Fill           string            `json:"fill"`                    // AnimationEffect's fill mode.
-	BackendNodeID  cdp.BackendNodeID `json:"backendNodeId"`           // AnimationEffect's target node.
+	BackendNodeID  cdp.BackendNodeID `json:"backendNodeId,omitempty"` // AnimationEffect's target node.
 	KeyframesRule  *KeyframesRule    `json:"keyframesRule,omitempty"` // AnimationEffect's keyframes.
 	Easing         string            `json:"easing"`                  // AnimationEffect's timing function.
 }
diff --git a/cmd/chromedp-gen/protocol.json b/cmd/chromedp-gen/protocol.json
index 504d864..4e20771 100644
--- a/cmd/chromedp-gen/protocol.json
+++ b/cmd/chromedp-gen/protocol.json
@@ -10456,11 +10456,6 @@
               "type": "number",
               "description": "<code>Animation</code>'s current time."
             },
-            {
-              "name": "source",
-              "$ref": "AnimationEffect",
-              "description": "<code>Animation</code>'s source animation node."
-            },
             {
               "name": "type",
               "type": "string",
@@ -10471,6 +10466,12 @@
               ],
               "description": "Animation type of <code>Animation</code>."
             },
+            {
+              "name": "source",
+              "$ref": "AnimationEffect",
+              "optional": true,
+              "description": "<code>Animation</code>'s source animation node."
+            },
             {
               "name": "cssId",
               "type": "string",
@@ -10523,6 +10524,7 @@
             {
               "name": "backendNodeId",
               "$ref": "DOM.BackendNodeId",
+              "optional": true,
               "description": "<code>AnimationEffect</code>'s target node."
             },
             {