fix(css): return undefined if there is no className

Author: logonoff

packages/react-core/src/components/Alert/__tests__/__snapshots__/AlertActionLink.test.tsx.snap

@@ -2,9 +2,7 @@
 
 exports[`Matches the snapshot 1`] = `
 <DocumentFragment>
-  <button
-    class=""
-  >
+  <button>
     Test
   </button>
   <p>

packages/react-core/src/components/List/__tests__/Generated/__snapshots__/ListItem.test.tsx.snap

@@ -2,9 +2,7 @@
 
 exports[`ListItem should match snapshot (auto-generated) 1`] = `
 <DocumentFragment>
-  <li
-    class=""
-  >
+  <li>
     <span>
       ReactNode
     </span>

packages/react-core/src/components/SearchInput/__tests__/__snapshots__/SearchInput.test.tsx.snap

@@ -2,9 +2,7 @@
 
 exports[`SearchInput advanced search 1`] = `
 <DocumentFragment>
-  <div
-    class=""
-  >
+  <div>
     <div
       class="pf-v6-c-input-group"
     >
@@ -145,7 +143,6 @@ exports[`SearchInput advanced search 1`] = `
 exports[`SearchInput advanced search with custom attributes 1`] = `
 <DocumentFragment>
   <div
-    class=""
     data-testid="test-id"
   >
     <div
@@ -478,9 +475,7 @@ exports[`SearchInput advanced search with custom attributes 1`] = `
 
 exports[`SearchInput renders search input in strict mode 1`] = `
 <DocumentFragment>
-  <div
-    class=""
-  >
+  <div>
     <div
       class="pf-v6-c-input-group"
     >

packages/react-core/src/components/ToggleGroup/__tests__/__snapshots__/ToggleGroupItemElement.test.tsx.snap

@@ -2,9 +2,7 @@
 
 exports[`empty 1`] = `
 <DocumentFragment>
-  <span
-    class=""
-  />
+  <span/>
 </DocumentFragment>
 `;
 

packages/react-styles/src/index.ts

@@ -2,8 +2,8 @@
  *
  * @param {any} args list of objects, string, or arrays to reduce
  */
-export function css(...args: any): string {
-  // Adapted from https://github.com/JedWatson/classnames/blob/master/index.js
+export function css(...args: any): string | undefined {
+  // Adapted from https://github.com/JedWatson/classnames/blob/main/index.js
   const classes = [] as string[];
   const hasOwn = {}.hasOwnProperty;
 
@@ -26,5 +26,5 @@ export function css(...args: any): string {
     }
   });
 
-  return classes.join(' ');
+  return classes.join(' ') || undefined;
 }