fix upload

Author: nachoab

file-uploader.html

@@ -135,7 +135,9 @@
 
       this.$.progressOverlay.currentFile = file;
 
-      (detail.xhrParamsPromise || Promise.resolve()).then(xhrParams => {
+      (detail.xhrParamsPromise || Promise.resolve({})).then(xhrParams => {
+        xhrParams.file = file;
+
         return this._xhr(xhrParams).then(response => {
           const data = {file, url: response.url};
 
@@ -198,6 +200,10 @@
           return reject(new Error('file-uploader requires an URL'));
         }
 
+        if (!file) {
+          return reject(new Error('file-uploader requires a file'));
+        }
+
         const xhr = new XMLHttpRequest();
 
         xhr.addEventListener('loadend', _ => {