Bug description
When the LazyLoadImage component is used in a component that is not visible in the window, the componentWillUnmount lifecycle method is called by React on it. If I do not scroll down to have it become visible and instead perform a navigation to a different page, the componentWillUnmount is called again, at which point this.placeholder is null (see screenshot, I added console.log at line 54 in resulting in src/components/PlaceholderWithoutTracking.jsx)

Uncaught TypeError: IntersectionObserver.unobserve: Argument 1 is not an object.

To Reproduce
Paste the code that is producing the issue

<LazyLoadImage key={idx} src={tool.image} alt={tool.name} effect={'blur'} /> 

Expected behavior
Navigation to next page to happen without error.

Screenshots

Technical details:

• Package version: 1.5.5
• Server Side Rendering: No
• Device: Any
• Operating System: Any
• Browser: Any