diff --git a/app/src/main/java/acr/browser/lightning/database/HistoryDatabase.java b/app/src/main/java/acr/browser/lightning/database/HistoryDatabase.java
index bc1895d..9676cac 100644
--- a/app/src/main/java/acr/browser/lightning/database/HistoryDatabase.java
+++ b/app/src/main/java/acr/browser/lightning/database/HistoryDatabase.java
@@ -89,7 +89,7 @@ public class HistoryDatabase extends SQLiteOpenHelper {
         }
     }
 
-    public synchronized void deleteHistoryItem(String url) {
+    public synchronized void deleteHistoryItem(@NonNull String url) {
         openIfNecessary();
         mDatabase.delete(TABLE_HISTORY, KEY_URL + " = ?", new String[]{url});
     }
@@ -118,7 +118,7 @@ public class HistoryDatabase extends SQLiteOpenHelper {
         mDatabase.insert(TABLE_HISTORY, null, values);
     }
 
-    synchronized String getHistoryItem(String url) {
+    synchronized String getHistoryItem(@NonNull String url) {
         openIfNecessary();
         Cursor cursor = mDatabase.query(TABLE_HISTORY, new String[]{KEY_ID, KEY_URL, KEY_TITLE},
                 KEY_URL + " = ?", new String[]{url}, null, null, null, null);
@@ -158,6 +158,7 @@ public class HistoryDatabase extends SQLiteOpenHelper {
         return itemList;
     }
 
+    @NonNull
     public synchronized List<HistoryItem> getLastHundredItems() {
         openIfNecessary();
         List<HistoryItem> itemList = new ArrayList<>(100);
@@ -180,6 +181,7 @@ public class HistoryDatabase extends SQLiteOpenHelper {
         return itemList;
     }
 
+    @NonNull
     public synchronized List<HistoryItem> getAllHistoryItems() {
         openIfNecessary();
         List<HistoryItem> itemList = new ArrayList<>();
diff --git a/app/src/main/java/acr/browser/lightning/object/SearchAdapter.java b/app/src/main/java/acr/browser/lightning/object/SearchAdapter.java
index 6c93bc5..316f7e2 100644
--- a/app/src/main/java/acr/browser/lightning/object/SearchAdapter.java
+++ b/app/src/main/java/acr/browser/lightning/object/SearchAdapter.java
@@ -209,7 +209,7 @@ public class SearchAdapter extends BaseAdapter implements Filterable {
 
     private static class ClearCacheRunnable implements Runnable {
 
-        private Application app;
+        private final Application app;
 
         public ClearCacheRunnable(Application app) {
             this.app = app;