update docs

packages/artplayer/src/scheme/validStringEmpty.js

@@ -0,0 +1,13 @@
+import { ArtPlayerError } from '../utils';
+
+export default function validStringEmpty(paths, value, type) {
+  if (type !== 'string') {
+    throw new ArtPlayerError(`${paths.join('.')} required 'string' type.`);
+  }
+
+  if (value.trim() === '') {
+    throw new ArtPlayerError(`${paths.join('.')} can not be empty`);
+  }
+
+  return true;
+}