diff --git a/app/src/main/java/org/fdroid/fdroid/installer/DefaultInstaller.java b/app/src/main/java/org/fdroid/fdroid/installer/DefaultInstaller.java
index 222256377..b806d5724 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/DefaultInstaller.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/DefaultInstaller.java
@@ -24,6 +24,7 @@ import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
+import android.support.annotation.NonNull;
 import org.fdroid.fdroid.data.Apk;
 
 /**
@@ -37,7 +38,7 @@ public class DefaultInstaller extends Installer {
 
     public static final String TAG = "DefaultInstaller";
 
-    DefaultInstaller(Context context, Apk apk) {
+    DefaultInstaller(Context context, @NonNull Apk apk) {
         super(context, apk);
     }
 
diff --git a/app/src/main/java/org/fdroid/fdroid/installer/ExtensionInstaller.java b/app/src/main/java/org/fdroid/fdroid/installer/ExtensionInstaller.java
index 8b710e00a..647ed89af 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/ExtensionInstaller.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/ExtensionInstaller.java
@@ -24,6 +24,7 @@ import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
+import android.support.annotation.NonNull;
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.data.Apk;
 import org.fdroid.fdroid.privileged.install.InstallExtensionDialogActivity;
@@ -44,7 +45,7 @@ import java.io.File;
 @Deprecated
 public class ExtensionInstaller extends Installer {
 
-    ExtensionInstaller(Context context, Apk apk) {
+    ExtensionInstaller(Context context, @NonNull Apk apk) {
         super(context, apk);
     }
 
diff --git a/app/src/main/java/org/fdroid/fdroid/installer/FileInstaller.java b/app/src/main/java/org/fdroid/fdroid/installer/FileInstaller.java
index 9356159aa..aa7d41d48 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/FileInstaller.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/FileInstaller.java
@@ -24,11 +24,12 @@ import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
 
+import android.support.annotation.NonNull;
 import org.fdroid.fdroid.data.Apk;
 
 public class FileInstaller extends Installer {
 
-    public FileInstaller(Context context, Apk apk) {
+    public FileInstaller(Context context, @NonNull Apk apk) {
         super(context, apk);
     }
 
diff --git a/app/src/main/java/org/fdroid/fdroid/installer/Installer.java b/app/src/main/java/org/fdroid/fdroid/installer/Installer.java
index 7d39269ba..38268e983 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/Installer.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/Installer.java
@@ -28,6 +28,7 @@ import android.content.pm.PackageManager;
 import android.net.Uri;
 import android.os.Build;
 import android.os.PatternMatcher;
+import android.support.annotation.NonNull;
 import android.support.v4.content.LocalBroadcastManager;
 import android.text.TextUtils;
 import org.fdroid.fdroid.Utils;
@@ -77,7 +78,7 @@ public abstract class Installer {
      * @param apk must be included so that all the phases of the install process
      *            can get all the data about the app, even after F-Droid was killed
      */
-    Installer(Context context, Apk apk) {
+    Installer(Context context, @NonNull Apk apk) {
         this.context = context;
         this.apk = apk;
     }
diff --git a/app/src/main/java/org/fdroid/fdroid/installer/InstallerFactory.java b/app/src/main/java/org/fdroid/fdroid/installer/InstallerFactory.java
index 072b1de74..12acd9079 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/InstallerFactory.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/InstallerFactory.java
@@ -21,8 +21,8 @@
 package org.fdroid.fdroid.installer;
 
 import android.content.Context;
+import android.support.annotation.NonNull;
 import android.text.TextUtils;
-
 import org.fdroid.fdroid.Utils;
 import org.fdroid.fdroid.data.Apk;
 
@@ -39,12 +39,11 @@ public class InstallerFactory {
      * @param apk     to be installed, always required.
      * @return instance of an Installer
      */
-    public static Installer create(Context context, Apk apk) {
-        if (apk == null || TextUtils.isEmpty(apk.packageName)) {
+    public static Installer create(Context context, @NonNull Apk apk) {
+        if (TextUtils.isEmpty(apk.packageName)) {
             throw new IllegalArgumentException("Apk.packageName must not be empty: " + apk);
         }
 
-
         Installer installer;
         if (!apk.isApk()) {
             Utils.debugLog(TAG, "Using FileInstaller for non-apk file");
diff --git a/app/src/main/java/org/fdroid/fdroid/installer/PrivilegedInstaller.java b/app/src/main/java/org/fdroid/fdroid/installer/PrivilegedInstaller.java
index 0bc880887..fee625af3 100644
--- a/app/src/main/java/org/fdroid/fdroid/installer/PrivilegedInstaller.java
+++ b/app/src/main/java/org/fdroid/fdroid/installer/PrivilegedInstaller.java
@@ -29,6 +29,7 @@ import android.content.pm.PackageManager;
 import android.net.Uri;
 import android.os.IBinder;
 import android.os.RemoteException;
+import android.support.annotation.NonNull;
 import android.util.Log;
 import org.fdroid.fdroid.Preferences;
 import org.fdroid.fdroid.R;
@@ -256,7 +257,7 @@ public class PrivilegedInstaller extends Installer {
                         "device owner has marked the package as uninstallable.");
     }
 
-    public PrivilegedInstaller(Context context, Apk apk) {
+    public PrivilegedInstaller(Context context, @NonNull Apk apk) {
         super(context, apk);
     }