'this._body is null' error during addChild

Hi,

I am attaching a project to this post here and I am wondering if anyone could tell me why I am getting a ‘this._body is null’ error after I instantiate a prefab and try to set it’s parent.

What I have is a PlatformSpawner component that initially instantiates a platform node, which continuously moves to the left the screen via its Rigidbody2D. There also an empty node in the middle of the screen that has its own collider so that when the platform touches it, a message is sent through my own event handler to the PlatformSpawner to instantiate another platform. However, I get the ‘this._body is null error’, which I’ve tracked down to when I try to set the platform as a child of any node, really.

I don’t understand the error because I have both a RigidBody2D and a BoxCollider2D set up on the platform.Any help would be appreciated. The error and code is below, while the project link is above. Thanks!

The error message:
error { target: Window, isTrusted: true, message: “TypeError: this._body is null”, filename: “http://localhost:7456/scripting/engine/bin/.cache/dev/preview/bundled/index.js”, lineno: 154773, colno: 11, error: TypeError, srcElement: Window, currentTarget: Window, eventPhase: 2, … }
​bubbles: true
​cancelBubble: false
​cancelable: true
​colno: 11
​composed: false
​currentTarget: null
​defaultPrevented: false
​error: TypeError: this._body is null
​eventPhase: 0
​explicitOriginalTarget: Window http://localhost:7456/
​filename: “http://localhost:7456/scripting/engine/bin/.cache/dev/preview/bundled/index.js
​isTrusted: true
​lineno: 154773
​message: “TypeError: this._body is null”
​originalTarget: Window http://localhost:7456/
​returnValue: true
​srcElement: Window http://localhost:7456/
​target: Window http://localhost:7456/
​timeStamp: 11130
​type: “error”
​<get isTrusted()>: function isTrusted()
​: ErrorEventPrototype { message: Getter, filename: Getter, lineno: Getter, … }
index.js:1:2554

Relevant code posted below:

@ccclass('ACEventHandler')
export class ACEventHandler extends Component {

    static instance:ACEventHandler;

    constructor() {
        super();
        if (ACEventHandler.instance) {
            return ACEventHandler.instance;
        }
        ACEventHandler.instance = this;
    }

    emitEvent(event:string, args?:any) {
        this.node.emit(event, args);
    }

    registerEvent(event:string, callback:any, bind:any) {
        this.node.on(event, callback, bind);
    }

    deregisterEvent(event:string, callback:any, bind:any) {
        this.node.off(event, callback, bind);
    }
}

@ccclass('Platform')
export class Platform extends Component {

    @property({type:Vec2})
    public force:Vec2 = new Vec2(-5, 0);

    private _rb:RigidBody2D|null = null;
    private _collider:BoxCollider2D|null = null;

    start () {
        if (!this._rb) {
            this._rb = this.getComponent(RigidBody2D);
        }

        if (!this._collider) {
            this._collider = this.getComponent(BoxCollider2D);
            this._collider?.on(Contact2DType.BEGIN_CONTACT, this.onBeginContact, this);
        }
    }

    lateUpdate(deltaTime:number) {
        if (this._rb) {
            this._rb.linearVelocity = this.force;
        }
    }

    onBeginContact(self:Collider2D, other:Collider2D, contact:IPhysics2DContact|null) {
        if (other.group === (1 << 4)) {
            ACEventHandler.instance?.emitEvent("spawn");
        }

        if (other.group == (1 << 5)) {
            this.node.destroy();
        }
    }
}

@ccclass('PlatformSpawner')
export class PlatformSpawner extends Component {

    @property({type:Prefab})
    public platformPrefab:Prefab|null = null;

    @property({type:Node})
    public spawnPoint:Node|null = null;

    private _speedMulitplier:number = 1;

    // This is called through a game manager when needed. It works.
    activate(active:boolean) {
        if (active) {
            ACEventHandler.instance?.registerEvent("spawn", this.spawnPlatform, this);
            this.spawnPlatform();
        }
        else {
            ACEventHandler.instance?.deregisterEvent("spawn", this.spawnPlatform, this);
        }
    }

    spawnPlatform() {
        if (this.platformPrefab) {
            let platform:Node = instantiate(this.platformPrefab);

            if (platform && this.spawnPoint) {
                this.node.addChild(platform); // WHY IS THERE A THIS._BODY IS NULL ERROR?
                platform.position = Vec3.ZERO;
            }
        }
    }
}