Fix retrieveDoc failing on empty URLs.

Author: BigBlueHat

playground/next/editor.mjs

@@ -395,6 +395,7 @@ window.app = createApp({
   },
   // methods
   async retrieveDoc(_editor, docVar, url) {
+    if (!url) return;
     try {
       const rv = await fetch(url);
       if (!rv.ok) {

playground/next/index.html

@@ -131,7 +131,7 @@ <h2 class="ui massive header">JSON-LD Playground</h2>
             <div class="ui icon input">
               <input type="text" placeholder="Document URL"
                 v-model="remoteDocURL" @keyup.enter="retrieveDoc(mainEditor, 'doc', remoteDocURL)">
-              <i class="file link icon" @click="retrieveDoc(mainEditor, 'doc', remoteDocURL)"></i>
+              <i class="file link icon" :class="{ disabled: remoteDocURL == '' }" @click="retrieveDoc(mainEditor, 'doc', remoteDocURL)"></i>
             </div>
           </div>
         </div>