Merge pull request #11806 from Snuffleupagus/pr-10738-followup

[api-minor] Fix the return value of `PDFDocumentProxy.getViewerPreferences` when no viewer preferences are present (PR 10738 follow-up)

src/core/obj.js

@@ -479,7 +479,7 @@ class Catalog {
     };
 
     const obj = this.catDict.get("ViewerPreferences");
-    const prefs = Object.create(null);
+    let prefs = null;
 
     if (isDict(obj)) {
       for (const key in ViewerPreferencesValidators) {
@@ -583,6 +583,9 @@ class Catalog {
         }
 
         if (prefValue !== undefined) {
+          if (!prefs) {
+            prefs = Object.create(null);
+          }
           prefs[key] = prefValue;
         } else {
           info(`Bad value in ViewerPreferences for "${key}".`);

src/display/api.js

@@ -663,7 +663,8 @@ class PDFDocumentProxy {
 
   /**
    * @returns {Promise} A promise that is resolved with an {Object} containing
-   *   the viewer preferences.
+   *   the viewer preferences, or `null` when no viewer preferences are present
+   *   in the PDF file.
    */
   getViewerPreferences() {
     return this._transport.getViewerPreferences();

test/unit/api_spec.js

@@ -24,7 +24,6 @@ import {
   createPromiseCapability,
   FontType,
   InvalidPDFException,
-  isEmptyObj,
   MissingPDFException,
   OPS,
   PasswordException,
@@ -846,9 +845,7 @@ describe("api", function () {
           return pdfDoc.getViewerPreferences();
         })
         .then(function (prefs) {
-          expect(
-            typeof prefs === "object" && prefs !== null && isEmptyObj(prefs)
-          ).toEqual(true);
+          expect(prefs).toEqual(null);
 
           loadingTask.destroy().then(done);
         })