fix always render comment for hydration

Author: marvinhagemeister

src/index.js

@@ -346,8 +346,10 @@ function _renderToString(
 				// Fragments are the least used components of core that's why
 				// branching here for comments has the least effect on perf.
 				return '<!--' + encodeEntities(props.UNSTABLE_comment) + '-->';
-			} else if ('dangerouslySetInnerHTML' in props) {
-				let html = props.dangerouslySetInnerHTML.__html ?? '';
+			}
+
+			if (props.dangerouslySetInnerHTML) {
+				let html = props.dangerouslySetInnerHTML.__html || '';
 				return '<!--$h-->' + html + '<!--/$h-->';
 			}
 

test/render.test.jsx

@@ -886,9 +886,25 @@ describe('render', () => {
 			let rendered = render(
 				<div>
 					foo
-					<Fragment dangerouslySetInnerHTML={{ __html: null }}>
-						<p>ignored</p>
-					</Fragment>
+					<Fragment dangerouslySetInnerHTML={{ __html: null }} />
+					baz
+				</div>
+			);
+			expect(rendered).to.equal('<div>foo<!--$h--><!--/$h-->baz</div>');
+
+			rendered = render(
+				<div>
+					foo
+					<Fragment dangerouslySetInnerHTML={{ __html: undefined }} />
+					baz
+				</div>
+			);
+			expect(rendered).to.equal('<div>foo<!--$h--><!--/$h-->baz</div>');
+
+			rendered = render(
+				<div>
+					foo
+					<Fragment dangerouslySetInnerHTML={{ __html: false }} />
 					baz
 				</div>
 			);