Bug: BarBounce/BarLeap animation crashes when `from` parameter is null

[xile611]

Description

BarBounce and BarLeap custom animation classes crash with TypeError: Cannot read properties of null (reading 'y1') when the from parameter is null or its properties are undefined.

Reproduction

Using VStory CDN (@visactor/vstory) to create a bar chart with barBounce effect:

<script src="https://unpkg.com/@visactor/vstory/dist/index.min.js"></script>
<script>
VStory.registerAll();
const dsl = {
  characters: [{
    type: "VChart",
    id: "bar1",
    zIndex: 1,
    position: { top: 50, left: 50, width: 500, height: 400 },
    options: {
      spec: {
        type: "bar",
        data: [{ values: [
          { x: "Q1", y: 120 },
          { x: "Q2", y: 180 }
        ]}],
        xField: "x",
        yField: "y"
      }
    }
  }],
  acts: [{
    id: "act1",
    scenes: [{
      id: "scene1",
      actions: [{
        characterId: "bar1",
        characterActions: [{
          action: "appear",
          payload: {
            animation: {
              duration: 1000,
              effect: "barBounce",    // ← triggers crash
              oneByOne: true
            }
          }
        }]
      }]
    }]
  }]
};
const story = new VStory.Story(dsl, { dom: "container" });
const player = new VStory.Player(story);
story.addAct(dsl.acts[0], dsl.characters, { character: {} });
player.play(0);
</script>

Error

Uncaught TypeError: Cannot read properties of null (reading 'y1')
    at new BarBounce (bar-bounce.ts:28)

Root Cause

In packages/vstory-animate/src/customAnimates/bar-bounce.ts, line 28-31:

constructor(
  from: { y?: number; y1?: number; x?: number; x1?: number },
  to: ...,
  ...
) {
  const f = {
    y: from.y1,    // ← crashes when from is null
    y1: from.y1,
    x: from.x1,
    x1: from.x1
  };
  super(f, { y: from.y, y1: from.y1, x: from.x, x1: from.x1 }, ...);
}

The type signature allows all properties to be optional, but the constructor body accesses them without null-safety. When VStory's animation system passes null as from (which happens when bar elements haven't been positioned yet), the constructor crashes.

BarLeap (bar-leap.ts) has a similar issue at line 90: this.to.x1! uses non-null assertion on an optional property.

Suggested Fix

Add null/undefined guards:

const f = {
  y: from?.y1 ?? 0,
  y1: from?.y1 ?? 0,
  x: from?.x1 ?? 0,
  x1: from?.x1 ?? 0
};

Environment

• VStory version: latest CDN (@visactor/vstory)
• Tested via unpkg CDN
• Browser: Chrome 131
• OS: macOS