animation.addClip(animationClip)偶尔报错，非常奇怪

Creator 2.x
#1

animation.addClip(animationClip)偶尔报错，报的错是下面：

CCAnimation.js:672 Uncaught TypeError: Cannot read property ‘length’ of null
at cc_Animation._createStates (CCAnimation.js:672)
at cc_Animation._init (CCAnimation.js:663)
at cc_Animation.addClip (CCAnimation.js:466)
at eval (eval at (quick_compile.js:238), :1681:19)
at utilities.js:344
at utils.js:81

通过日志观察animation和animationClip这两个变量都不是null，但很奇怪为啥会在这里崩溃？请有过这种经历的老师多指教，谢谢！

#2

进一步跟踪进引擎的结果是：下面函数的 for (let i = 0; i < this._clips.length; ++i) { 这一步报错了，似乎是没有_clips。但还是一头雾水，毕竟是引擎里面的函数，我搞不清为什么这里会报错

_createStates: function() {
    this._nameToState = js.createMap(true);

    // create animation states
    let state = null;
    let defaultClipState = false;
    for (let i = 0; i < this._clips.length; ++i) {
        let clip = this._clips[i];
        if (clip) {
            state = new cc.AnimationState(clip);

            if (CC_EDITOR) {
                this._animator._reloadClip(state);
            }

            this._nameToState[state.name] = state;
            if (equalClips(this._defaultClip, clip)) {
                defaultClipState = state;
            }
        }
    }
    if (this._defaultClip && !defaultClipState) {
        state = new cc.AnimationState(this._defaultClip);

        if (CC_EDITOR) {
            this._animator._reloadClip(state);
        }

        this._nameToState[state.name] = state;
    }
}

});

#3

有时候还报下面的错误，都是在animation.addClip(animationClip)这句话，有点怀疑是开发工具的bug，真头疼死了。。。。

js.js:814 Uncaught TypeError: Cannot read property ‘indexOf’ of null
at Object.contains (js.js:814)
at cc_Animation.addClip (CCAnimation.js:469)
at eval (eval at (quick_compile.js:238), :1694:19)
at utilities.js:344
at utils.js:81