fix(runtime): omit absent src attribute value

Author: dangreen

packages/runtime/README.md

@@ -52,7 +52,7 @@ import url, { src, srcSet } from './photo.jpg'
 import { getImageProps, getSourceProps } from '@srcset/runtime'
 
 const { src: imgSrc, srcSet: imgSrcSet } = getImageProps(src, srcSet)
-// <img src={imgSrc} srcset={imgSrcSet}/>
+// <img src={imgSrc} srcSet={imgSrcSet}/>
 
 const sources = getSourceProps(srcSet)
 // sources of <picture>, grouped by mime type and ordered by format efficiency

packages/runtime/src/attributes.ts

@@ -55,10 +55,14 @@ export interface ImageSrcProps {
  */
 export function getImageProps(src: SrcSetEntry | undefined, srcSet: SrcSetEntry[] | string | undefined): ImageSrcProps {
   if (typeof srcSet === 'string') {
-    return {
-      src: src?.url,
-      srcSet
-    }
+    return src
+      ? {
+        src: src.url,
+        srcSet
+      }
+      : {
+        srcSet
+      }
   }
 
   if (!src) {