Restore Frame Buffer

dist/preview release/customConfigurations/minimalViewer/babylon.max.js

@@ -8289,7 +8289,9 @@ var BABYLON;
         Engine.prototype.restoreDefaultFramebuffer = function () {
             this._currentRenderTarget = null;
             this.bindUnboundFramebuffer(null);
-            this.setViewport(this._cachedViewport);
+            if (this._cachedViewport) {
+                this.setViewport(this._cachedViewport);
+            }
             this.wipeCaches();
         };
         // UBOs

src/babylon.engine.ts

@@ -1428,8 +1428,9 @@
         public restoreDefaultFramebuffer(): void {
             this._currentRenderTarget = null;
             this.bindUnboundFramebuffer(null);
-
-            this.setViewport(this._cachedViewport);
+            if (this._cachedViewport) {
+                this.setViewport(this._cachedViewport);
+            }
 
             this.wipeCaches();
         }