Add support for null/undefined values in array classnames

src/kaiku.ts

@@ -254,7 +254,12 @@ type Render = <PropertiesT extends DefaultProps>(
   rootElement: HTMLElement | SVGElement
 ) => void
 
-type ClassNames = string | { [key: string]: boolean } | ClassNames[]
+type ClassNames =
+  | undefined
+  | null
+  | string
+  | { [key: string]: boolean }
+  | ClassNames[]
 
 //
 //  Generic utilities
@@ -1161,6 +1166,10 @@ const destroyLazyUpdates = (instance: HtmlElementInstance) => {
 ///////////////
 
 const stringifyClassNames = (names: ClassNames): string => {
+  if (names === null || typeof names === 'undefined') {
+    return ''
+  }
+
   if (typeof names === 'string') {
     return names
   }

test/__snapshots__/kaiku.spec.tsx.snap

@@ -14,6 +14,10 @@ exports[`kaiku should be able to access this.props 1`] = `"<div>hello</div>"`;
 
 exports[`kaiku should be able to inject raw HTML 1`] = `"<div><div>foo<span>bar</span></div></div>"`;
 
+exports[`kaiku should handle array of classnames including \`null\` 1`] = `"<div class=\\"\\"></div>"`;
+
+exports[`kaiku should handle array of classnames including \`undefined\` 1`] = `"<div class=\\"\\"></div>"`;
+
 exports[`kaiku should handle changing rootNode.firstChild 1`] = `"<div>Hello, I am a div tag!</div>"`;
 
 exports[`kaiku should handle changing rootNode.firstChild 2`] = `"<span>Hello, I am a span tag!</span>"`;

test/kaiku.spec.tsx

@@ -1945,4 +1945,22 @@ describe('kaiku', () => {
     render(<App />, rootNode)
     expect(rootNode.innerHTML).toMatchSnapshot()
   })
+
+  it('should handle array of classnames including `undefined`', async () => {
+    const App = () => {
+      return <div class={[undefined]} />
+    }
+
+    render(<App />, rootNode)
+    expect(rootNode.innerHTML).toMatchSnapshot()
+  })
+
+  it('should handle array of classnames including `null`', async () => {
+    const App = () => {
+      return <div class={[null]} />
+    }
+
+    render(<App />, rootNode)
+    expect(rootNode.innerHTML).toMatchSnapshot()
+  })
 })