Fixing nullable problems

app/src/main/java/acr/browser/lightning/database/BookmarkManager.java

@@ -447,7 +447,7 @@ public class BookmarkManager {
      *
      * @return the current folder
      */
-    @Nullable
+    @NonNull
     public String getCurrentFolder() {
         return mCurrentFolder;
     }

app/src/main/java/acr/browser/lightning/database/HistoryItem.java

@@ -63,7 +63,7 @@ public class HistoryItem implements Comparable<HistoryItem> {
         this.mImageId = id;
     }
 
-    public void setBitmap(Bitmap image) {
+    public void setBitmap(@Nullable Bitmap image) {
         mBitmap = image;
     }