Error thrown with Preact8

.travis.yml

@@ -8,3 +8,5 @@ env:
   -
   - PREACT_VERSION=5.7.0
   - PREACT_VERSION=6.0.2
+  - PREACT_VERSION=7.2.1
+  - PREACT_VERSION=8.1.0

src/CSSTransitionGroup.js

@@ -12,7 +12,7 @@
 
 
 import { h, cloneElement, Component } from 'preact';
-import { getKey } from './util';
+import { getKey, filterNullChildren } from './util';
 import { mergeChildMappings, isShownInChildren, isShownInChildrenByKey, inChildren, inChildrenByKey } from './TransitionChildMapping';
 import { CSSTransitionGroupChild } from './CSSTransitionGroupChild';
 
@@ -42,10 +42,10 @@ export class CSSTransitionGroup extends Component {
 	}
 
 	componentWillReceiveProps({ children, exclusive, showProp }) {
-		let nextChildMapping = (children || []).slice();
+		let nextChildMapping = filterNullChildren(children || []).slice();
 
 		// last props children if exclusive
-		let prevChildMapping = exclusive ? this.props.children : this.state.children;
+		let prevChildMapping = filterNullChildren(exclusive ? this.props.children : this.state.children);
 
 		let newChildren = mergeChildMappings(
 			prevChildMapping,
@@ -118,7 +118,7 @@ export class CSSTransitionGroup extends Component {
 
 	_handleDoneEntering(key) {
 		delete this.currentlyTransitioningKeys[key];
-		let currentChildMapping = this.props.children,
+		let currentChildMapping = filterNullChildren(this.props.children),
 			showProp = this.props.showProp;
 		if (!currentChildMapping || (
 			!showProp && !inChildrenByKey(currentChildMapping, key)
@@ -157,7 +157,7 @@ export class CSSTransitionGroup extends Component {
 	_handleDoneLeaving(key) {
 		delete this.currentlyTransitioningKeys[key];
 		let showProp = this.props.showProp,
-			currentChildMapping = this.props.children;
+			currentChildMapping = filterNullChildren(this.props.children);
 		if (showProp && currentChildMapping &&
 			isShownInChildrenByKey(currentChildMapping, key, showProp)) {
 			this.performEnter(key);
@@ -200,7 +200,7 @@ export class CSSTransitionGroup extends Component {
 	render({ component:Component, transitionName, transitionEnter, transitionLeave, children:c, ...props }, { children }) {
 		return (
 			<Component {...props}>
-				{ children.map(this.renderChild) }
+				{ filterNullChildren(children).map(this.renderChild) }
 			</Component>
 		);
 	}

src/util.js

@@ -9,3 +9,7 @@ export function getComponentBase(component) {
 export function onlyChild(children) {
 	return children && children[0];
 }
+
+export function filterNullChildren(children) {
+	return children && children.filter(i => i !== null);
+}

tests/index.js

@@ -83,6 +83,40 @@ class SVGList extends Component {
 	}
 }
 
+class NullChildren extends Component {
+
+	state = {
+		items: [
+			{ displayed: true, item: 'hello'},
+			{ displayed: true, item: 'world'},
+			{ displayed: false, item: 'click'},
+			{ displayed: true, item: 'me'}
+		]
+	};
+
+	toggleDisplay(i) {
+		let { items } = this.state;
+		const item = items[i];
+		item.displayed = !item.displayed;
+		this.setState({ items });
+	}
+
+	render(_, { items }) {
+		return (
+			<div className='root'>
+				<CSSTransitionGroup transitionName="example">
+					{null}
+
+					{ items.map( ({displayed, item}, i) => (
+						displayed ? <Todo key={item} onClick={this.toggleDisplay.bind(this, i)}>
+							{item}
+						</Todo> : null
+					)) }
+				</CSSTransitionGroup>
+			</div>
+		);
+	}
+}
 
 const Nothing = () => null;
 
@@ -204,3 +238,63 @@ describe('CSSTransitionGroup: SVG', () => {
 		}, 1400);
 	});
 });
+
+describe('CSSTransitionGroup: NullChildren', () => {
+	let container = document.createElement('div'),
+		list, root;
+	document.body.appendChild(container);
+
+	let $ = s => [].slice.call(container.querySelectorAll(s));
+
+	beforeEach( () => {
+		root = render(<div><Nothing /></div>, container, root);
+		root = render(<div><NullChildren ref={c => list=c} /></div>, container, root);
+	});
+
+	afterEach( () => {
+		list = null;
+	});
+
+	it('create works', () => {
+		expect($('.item')).to.have.length(3);
+	});
+
+	it('transitionLeave works', done => {
+		// this.timeout(5999);
+		list.toggleDisplay(1);
+
+		// make sure -leave class was added
+		setTimeout( () => {
+			expect($('.item')).to.have.length(3);
+
+			expect($('.item')[1].className).to.contain('example-leave');
+			expect($('.item')[1].className).to.contain('example-leave-active');
+		}, 100);
+
+		// then make sure it's gone
+		setTimeout( () => {
+			expect($('.item')).to.have.length(2);
+			done();
+		}, 1400);
+	});
+
+	it('transitionEnter works', done => {
+		// this.timeout(5999);
+		list.toggleDisplay(2);
+
+		setTimeout( () => {
+			expect($('.item')).to.have.length(4);
+			expect($('.item')[2].className).to.contain('example-enter');
+			expect($('.item')[2].className).to.contain('example-enter-active');
+		}, 500);
+
+		setTimeout( () => {
+			expect($('.item')).to.have.length(4);
+
+			expect($('.item')[3].className).not.to.contain('example-enter');
+			expect($('.item')[3].className).not.to.contain('example-enter-active');
+
+			done();
+		}, 1400);
+	});
+});