Toast when no app can be found matching id

res/values/strings.xml

@@ -29,6 +29,7 @@
 	<string name="app_name">F-Droid</string>
     <string name="search_results">Search Results</string>
     <string name="app_details">App Details</string>
+    <string name="no_such_app">No matching app was found in the database.</string>
 
 	<string name="about_title">About F-Droid</string>
 	<string name="about_desc">Originally based on Aptoide.\nReleased under the

src/org/fdroid/fdroid/AppDetails.java

@@ -324,6 +324,9 @@ public class AppDetails extends ListActivity {
             }
         }
         if (app == null) {
+            Toast toast = Toast.makeText(this,
+                    getString(R.string.no_such_app), Toast.LENGTH_LONG);
+            toast.show();
             finish();
             return false;
         }