diff --git a/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkDatabase.java b/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkDatabase.java
index 3bfcf1f..cfe7174 100644
--- a/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkDatabase.java
+++ b/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkDatabase.java
@@ -142,6 +142,8 @@ public class BookmarkDatabase extends SQLiteOpenHelper implements BookmarkModel
 
                 if (cursor.moveToFirst()) {
                     subscriber.onItem(bindCursorToHistoryItem(cursor));
+                } else {
+                    subscriber.onItem(null);
                 }
 
                 cursor.close();
diff --git a/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkModel.java b/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkModel.java
index 9d27d2c..d4cb905 100644
--- a/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkModel.java
+++ b/app/src/main/java/acr/browser/lightning/database/bookmark/BookmarkModel.java
@@ -19,42 +19,136 @@ import acr.browser.lightning.database.HistoryItem;
  */
 public interface BookmarkModel {
 
+    /**
+     * Gets the bookmark associated with the URL.
+     *
+     * @param url the URL to look for.
+     * @return an observable that will emit either
+     * the bookmark associated with the URL or null.
+     */
     @NonNull
     Single<HistoryItem> findBookmarkForUrl(@NonNull String url);
 
+    /**
+     * Determines if a URL is associated with a bookmark.
+     *
+     * @param url the URL to check.
+     * @return an observable that will emit true if
+     * the URL is a bookmark, false otherwise.
+     */
     @NonNull
     Single<Boolean> isBookmark(@NonNull String url);
 
+    /**
+     * Adds a bookmark if one does not already exist with
+     * the same URL.
+     *
+     * @param item the bookmark to add.
+     * @return an observable that emits true if the bookmark
+     * was added, false otherwise.
+     */
     @NonNull
     Single<Boolean> addBookmarkIfNotExists(@NonNull HistoryItem item);
 
+    /**
+     * Adds a list of bookmarks to the database.
+     *
+     * @param bookmarkItems the bookmarks to add.
+     * @return an observable that emits a complete event
+     * when all the bookmarks have been added.
+     */
     @NonNull
     Completable addBookmarkList(@NonNull List<HistoryItem> bookmarkItems);
 
+    /**
+     * Deletes a bookmark from the database.
+     *
+     * @param bookmark the bookmark to delete.
+     * @return an observable that emits true when
+     * the bookmark is deleted, false otherwise.
+     */
     @NonNull
     Single<Boolean> deleteBookmark(@NonNull HistoryItem bookmark);
 
+    /**
+     * Moves all bookmarks in the old folder to the new folder.
+     *
+     * @param oldName the name of the old folder.
+     * @param newName the name of the new folder.
+     * @return an observable that emits a completion
+     * event when the folder is renamed.
+     */
     @NonNull
     Completable renameFolder(@NonNull String oldName, @NonNull String newName);
 
+    /**
+     * Deletes a folder from the database, all bookmarks
+     * in that folder will be moved to the root level.
+     *
+     * @param folderToDelete the folder to delete.
+     * @return an observable that emits a completion
+     * event when the folder has been deleted.
+     */
     @NonNull
     Completable deleteFolder(@NonNull String folderToDelete);
 
+    /**
+     * Deletes all bookmarks in the database.
+     *
+     * @return an observable that emits a completion
+     * event when all bookmarks have been deleted.
+     */
     @NonNull
     Completable deleteAllBookmarks();
 
+    /**
+     * Changes the bookmark with the original URL
+     * with all the data from the new bookmark.
+     *
+     * @param oldBookmark the old bookmark to replace.
+     * @param newBookmark the new bookmark.
+     * @return an observable that emits a completion event
+     * when the bookmark edit is done.
+     */
     @NonNull
     Completable editBookmark(@NonNull HistoryItem oldBookmark, @NonNull HistoryItem newBookmark);
 
+    /**
+     * Emits a list of all bookmarks
+     *
+     * @return an observable that emits a list
+     * of all bookmarks.
+     */
     @NonNull
     Single<List<HistoryItem>> getAllBookmarks();
 
+    /**
+     * Emits all bookmarks in a certain folder.
+     * If the folder chosen is null, then all bookmarks
+     * without a specified folder will be returned.
+     *
+     * @param folder gets the bookmarks from this folder, may be null.
+     * @return an observable that emits a list of bookmarks
+     * in the given folder.
+     */
     @NonNull
     Single<List<HistoryItem>> getBookmarksFromFolder(@Nullable String folder);
 
+    /**
+     * Returns all folders as {@link HistoryItem}.
+     * The root folder is omitted.
+     *
+     * @return an observable that emits a list of folders.
+     */
     @NonNull
     Single<List<HistoryItem>> getFolders();
 
+    /**
+     * Returns the names of all folders.
+     * The root folder is omitted.
+     *
+     * @return an observable that emits a list of folder names.
+     */
     @NonNull
     Single<List<String>> getFolderNames();
 }