fix: children.map when new child return null

src/index.js

@@ -185,12 +185,26 @@ function unmountComponentAtNode(container) {
 const ARR = [];
 
 // This API is completely unnecessary for Preact, so it's basically passthrough.
+
 let Children = {
 	map(children, fn, ctx) {
 		if (children == null) return null;
 		children = Children.toArray(children);
 		if (ctx && ctx!==children) fn = fn.bind(ctx);
-		return children.map(fn);
+		const newChildren = [];
+
+		children.forEach((old, index) => {
+			if (old === void 0 || old === false || old === true) {
+				old = null;
+			}
+			const newChild = fn(old, index);
+			if (newChild == null) { // when the return value is null, ignore
+				return;
+			}
+			newChildren.push(newChild);
+		});
+
+		return newChildren;
 	},
 	forEach(children, fn, ctx) {
 		if (children == null) return null;
@@ -592,7 +606,7 @@ PureComponent.prototype.shouldComponentUpdate = function(props, state) {
 };
 
 function unstable_batchedUpdates(callback) {
-  callback();
+	callback();
 }
 
 export {

test/component.js

@@ -543,4 +543,36 @@ describe('components', () => {
 			expect(spy).not.to.have.been.called;
 		});
 	});
+
+	describe('ReactChildren', () => {
+		it("should ignore when child return null", () => {
+			let zero = <div key="keyZero" />;
+			let one = null;
+			let two = <div key="keyTwo" />;
+			let three = null;
+			let four = <div key="keyFour" />;
+
+			let mapped = [
+				<div key="giraffe" />, // Key should be joined to obj key
+				null, // Key should be added even if we don't supply it!
+				<div />, // Key should be added even if not supplied!
+				<span />, // Map from null to something.
+				<div key="keyFour" />
+			];
+			let instance = (
+					<div>
+						{zero}
+						{one}
+						{two}
+						{three}
+						{four}
+					</div>
+			);
+			const mappedChildren = React.Children.map(instance.props.children, (kid, index) => mapped[index]);
+			expect(mappedChildren[0]).to.equal(<div key="giraffe" />);
+			expect(mappedChildren[1]).to.equal(<div/>);
+			expect(mappedChildren[2]).to.equal(<span/>);
+			expect(mappedChildren[3]).to.equal(<div key="keyFour" />);
+		});
+	});
 });