render empty string for null __html

.changeset/yellow-ghosts-bow.md

@@ -0,0 +1,5 @@
+---
+'preact-render-to-string': patch
+---
+
+Correctly render `null` as an `__html` value as an empty string

src/index.js

@@ -590,7 +590,7 @@ function _renderToString(
 				break;
 
 			case 'dangerouslySetInnerHTML':
-				html = v && v.__html;
+				html = v && v.__html != null ? v.__html : '';
 				continue;
 
 			// serialize object styles to a CSS string

test/render.test.jsx

@@ -387,6 +387,16 @@ describe('render', () => {
 			);
 		});
 
+		it('should accept nullish __html', () => {
+			const Test = (props) => (
+				<Fragment>
+					<div>hi</div>
+					<div dangerouslySetInnerHTML={{ __html: null }} />
+				</Fragment>
+			);
+			expect(render(<Test />)).to.equal('<div>hi</div><div></div>');
+		});
+
 		it('should apply defaultProps', () => {
 			const Test = (props) => <div {...props} />;
 			Test.defaultProps = {