fix: preserve default className when className is null or undefined

[Shiva903-hue]

What does this PR do?

Preserves the default react-tabs className in UncontrolledTabs when
props.className is undefined or null.

Why?

Currently, spreading { ...defaultProps, ...props } causes an explicit
undefined or null className to override the default, which breaks
backward compatibility and styling.

Maintainers confirmed this behavior in #581.

What’s included

• Guard against undefined / null overrides
• Regression tests covering both cases

Related issue

Fixes #581

[danez]

Thanks for the PR.

I left some comments.

[danez]

This domAttributes is not needed. We remove all custom props above and pass on everything else.

Suggested change

	// Only pass valid DOM attributes and data- attributes
	const domAttributes = {};
	Object.keys(restProps).forEach((key) => {
	if (
	key.startsWith('data-') ||
	key === 'id' ||
	key === 'style' ||
	key === 'title' ||
	key === 'role' ||
	key === 'tabIndex' ||
	key === 'aria-label' ||
	key === 'aria-labelledby' ||
	key === 'aria-describedby' ||
	key === 'aria-controls' ||
	key === 'aria-selected' ||
	key === 'aria-disabled'
	) {
	domAttributes[key] = restProps[key];
	}
	});

[danez]

Suggested change

	{...domAttributes}
	{...attributes}

[danez]

Suggested change

	...restProps
	...attributes

[danez]

Suggested change

	const className =
	propClassName == null ? defaultProps.className : propClassName;
	const className = propClassName ?? defaultProps.className;