diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/BtLEAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/BtLEAction.java
index 7e630ae4ef..bf7a25eca9 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/BtLEAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/BtLEAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Carsten Pfeiffer, Uwe Hermann
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer, Uwe Hermann, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -19,15 +19,19 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle;
 import android.bluetooth.BluetoothGatt;
 import android.bluetooth.BluetoothGattCharacteristic;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import nodomain.freeyourgadget.gadgetbridge.util.DateTimeUtils;
 
 /**
  * The Bluedroid implementation only allows performing one GATT request at a time.
  * As they are asynchronous anyway, we encapsulate every GATT request (read and write)
  * inside a runnable action.
- * <p/>
+ * <p>
  * These actions are then executed one after another, ensuring that every action's result
  * has been posted before invoking the next action.
+ * </p>
  */
 public abstract class BtLEAction {
     private final BluetoothGattCharacteristic characteristic;
@@ -41,33 +45,36 @@ public abstract class BtLEAction {
     /**
      * Returns true if this action expects an (async) result which must
      * be waited for, before continuing with other actions.
-     * <p/>
+     * <p>
      * This is needed because the current Bluedroid stack can only deal
      * with one single bluetooth operation at a time.
+     * </p>
      */
     public abstract boolean expectsResult();
 
     /**
-     * Executes this action, e.g. reads or write a GATT characteristic.
+     * Executes this action, e.g. reads or write a {@link GattCharacteristic}.
      *
-     * @param gatt the characteristic to manipulate, or null if none.
-     * @return true if the action was successful, false otherwise
+     * @return {@code true} if the action was successful, {@code false} otherwise
      */
-    public abstract boolean run(BluetoothGatt gatt);
+    public abstract boolean run(@NonNull BluetoothGatt gatt);
 
     /**
      * Returns the GATT characteristic being read/written/...
      *
-     * @return the GATT characteristic, or <code>null</code>
+     * @return the GATT characteristic, or {@code null}
      */
+    @Nullable
     public BluetoothGattCharacteristic getCharacteristic() {
         return characteristic;
     }
 
+    @NonNull
     protected String getCreationTime() {
         return DateTimeUtils.formatLocalTime(creationTimestamp);
     }
 
+    @NonNull
     public String toString() {
         BluetoothGattCharacteristic characteristic = getCharacteristic();
         String uuid = characteristic == null ? "(null)" : characteristic.getUuid().toString();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/AbortTransactionAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/AbortTransactionAction.java
index 12bbe68324..579a6e9b50 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/AbortTransactionAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/AbortTransactionAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Carsten Pfeiffer
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer
 
     This file is part of Gadgetbridge.
 
@@ -18,6 +18,8 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 
 import android.bluetooth.BluetoothGatt;
 
+import androidx.annotation.NonNull;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -29,7 +31,7 @@ public abstract class AbortTransactionAction extends PlainAction {
     private static final Logger LOG = LoggerFactory.getLogger(AbortTransactionAction.class);
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         if (shouldAbort()) {
             LOG.info("Aborting transaction because abort criteria met.");
             return false;
@@ -39,6 +41,7 @@ public abstract class AbortTransactionAction extends PlainAction {
 
     protected abstract boolean shouldAbort();
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + " abort=" + shouldAbort();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/BondAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/BondAction.java
index 9102470835..f6bb1fe037 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/BondAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/BondAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2023-2025 Andreas Böhler, Thomas Kuehne
+/*  Copyright (C) 2023-2026 Andreas Böhler, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -22,6 +22,7 @@ import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.IntentFilter;
 
+import androidx.annotation.NonNull;
 import androidx.core.content.ContextCompat;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
@@ -70,7 +71,7 @@ public class BondAction extends PlainAction implements BondingInterface {
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         BluetoothDevice device = gatt.getDevice();
         mCandidate = new GBDeviceCandidate(device, GBDevice.RSSI_UNKNOWN, null, null);
         BondingUtil.tryBondThenComplete(this, device);
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/CheckInitializedAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/CheckInitializedAction.java
index 3dc83b5d01..2d4829d706 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/CheckInitializedAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/CheckInitializedAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2016-2024 Carsten Pfeiffer
+/*  Copyright (C) 2016-2026 Carsten Pfeiffer
 
     This file is part of Gadgetbridge.
 
@@ -16,6 +16,8 @@
     along with this program.  If not, see <https://www.gnu.org/licenses/>. */
 package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 
+import androidx.annotation.NonNull;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -29,9 +31,10 @@ import nodomain.freeyourgadget.gadgetbridge.impl.GBDevice;
 public class CheckInitializedAction extends AbortTransactionAction {
     private static final Logger LOG = LoggerFactory.getLogger(CheckInitializedAction.class);
 
+    @NonNull
     private final GBDevice device;
 
-    public CheckInitializedAction(GBDevice gbDevice) {
+    public CheckInitializedAction(@NonNull GBDevice gbDevice) {
         device = gbDevice;
     }
 
@@ -39,7 +42,7 @@ public class CheckInitializedAction extends AbortTransactionAction {
     protected boolean shouldAbort() {
         boolean abort = device.isInitialized();
         if (abort) {
-            LOG.info("Aborting device initialization, because already initialized: " + device);
+            LOG.info("Aborting device initialization, because already initialized: {}", device);
         }
         return abort;
     }
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ConditionalWriteAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ConditionalWriteAction.java
index 623b6eae82..82d6474d05 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ConditionalWriteAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ConditionalWriteAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2016-2025 Andreas Shimokawa, Carsten Pfeiffer, Thomas Kuehne
+/*  Copyright (C) 2016-2026 Andreas Shimokawa, Carsten Pfeiffer, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -19,16 +19,19 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 import android.bluetooth.BluetoothGatt;
 import android.bluetooth.BluetoothGattCharacteristic;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 public abstract class ConditionalWriteAction extends WriteAction {
     private boolean actualGenerated;
     private byte[] actual;
 
-    public ConditionalWriteAction(BluetoothGattCharacteristic characteristic) {
+    public ConditionalWriteAction(@NonNull BluetoothGattCharacteristic characteristic) {
         super(characteristic, null);
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         byte[] value = getValue();
         if (value != null) {
             return super.run(gatt);
@@ -47,12 +50,14 @@ public abstract class ConditionalWriteAction extends WriteAction {
 
     /**
      * Checks the condition whether the write shall happen or not.
-     * Returns the actual value to be written or null in case nothing shall be written.
-     * <p/>
-     * Note that returning null will not cause {@link #run()} to return false, in other words,
+     * Returns the actual value to be written or {@code null} in case nothing shall be written.
+     * <p>
+     * Note that returning {@code null} will not cause {@link #run(BluetoothGatt)} to return {@code false}, in other words,
      * the rest of the queue will still be executed.
+     * </p>
      *
-     * @return the value to be written or null to not write anything
+     * @return the value to be written or {@code null} to not write anything
      */
+    @Nullable
     protected abstract byte[] checkCondition();
 }
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/FunctionAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/FunctionAction.java
index 4c6c32214b..ca42596e1d 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/FunctionAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/FunctionAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2023-2025 Johannes Krude, Thomas Kuehne
+/*  Copyright (C) 2023-2026 Johannes Krude, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -50,7 +50,7 @@ public class FunctionAction extends BtLEAction {
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         try {
             final boolean success;
             if (mRunnable != null) {
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/NotifyAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/NotifyAction.java
index 55d9de226d..1137e5a695 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/NotifyAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/NotifyAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Alicia Hormann, Carsten Pfeiffer, Daniele Gobbetti
+/*  Copyright (C) 2015-2026 Alicia Hormann, Carsten Pfeiffer, Daniele Gobbetti
 
     This file is part of Gadgetbridge.
 
@@ -32,6 +32,8 @@ import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCallback;
 
 import static nodomain.freeyourgadget.gadgetbridge.service.btle.GattDescriptor.UUID_DESCRIPTOR_GATT_CLIENT_CHARACTERISTIC_CONFIGURATION;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.RequiresPermission;
 
 /**
@@ -43,16 +45,19 @@ public class NotifyAction extends BtLEAction {
 
     private static final Logger LOG = LoggerFactory.getLogger(NotifyAction.class);
     private final boolean enableFlag;
-    private boolean hasWrittenDescriptor = false;
+    private boolean hasWrittenDescriptor;
 
-    public NotifyAction(BluetoothGattCharacteristic characteristic, boolean enable) {
+    public NotifyAction(@NonNull BluetoothGattCharacteristic characteristic, boolean enable) {
         super(characteristic);
         enableFlag = enable;
+        hasWrittenDescriptor = false;
     }
 
     /// shared write implementation that can be used without a BtLEAction
     @SuppressLint("MissingPermission")
-    public static boolean writeDescriptor(final BluetoothGatt gatt, final BluetoothGattDescriptor descriptor, final byte[] value) {
+    public static boolean writeDescriptor(@Nullable final BluetoothGatt gatt,
+                                          @Nullable final BluetoothGattDescriptor descriptor,
+                                          @NonNull final byte[] value) {
         if (gatt == null) {
             LOG.error("gatt == null");
             return false;
@@ -96,7 +101,7 @@ public class NotifyAction extends BtLEAction {
 
     @Override
     @RequiresPermission("android.permission.BLUETOOTH_CONNECT")
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         // register gatt's callback to receive notifications
         boolean result = gatt.setCharacteristicNotification(getCharacteristic(), enableFlag);
 
@@ -137,6 +142,7 @@ public class NotifyAction extends BtLEAction {
         return hasWrittenDescriptor;
     }
 
+    @NonNull
     @Override
     public String toString() {
         BluetoothGattCharacteristic characteristic = getCharacteristic();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/PlainAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/PlainAction.java
index 5dc25c2c02..4ad91fd5c3 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/PlainAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/PlainAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Carsten Pfeiffer
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer
 
     This file is part of Gadgetbridge.
 
@@ -16,6 +16,8 @@
     along with this program.  If not, see <https://www.gnu.org/licenses/>. */
 package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 
+import androidx.annotation.NonNull;
+
 import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEAction;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCharacteristic;
 
@@ -34,6 +36,7 @@ public abstract class PlainAction extends BtLEAction {
         return false;
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadAction.java
index 1cfcaf1e47..bfb15e1965 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Carsten Pfeiffer, Daniele Gobbetti
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer, Daniele Gobbetti
 
     This file is part of Gadgetbridge.
 
@@ -20,6 +20,8 @@ import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothGatt;
 import android.bluetooth.BluetoothGattCharacteristic;
 
+import androidx.annotation.NonNull;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -34,13 +36,13 @@ import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCallback;
 public class ReadAction extends BtLEAction {
     private static final Logger LOG = LoggerFactory.getLogger(ReadAction.class);
 
-    public ReadAction(BluetoothGattCharacteristic characteristic) {
+    public ReadAction(@NonNull BluetoothGattCharacteristic characteristic) {
         super(characteristic);
     }
 
     @SuppressLint("MissingPermission")
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         int properties = getCharacteristic().getProperties();
         if ((properties & BluetoothGattCharacteristic.PROPERTY_READ) > 0) {
             return gatt.readCharacteristic(getCharacteristic());
@@ -54,6 +56,7 @@ public class ReadAction extends BtLEAction {
         return true;
     }
 
+    @NonNull
     @Override
     public String toString() {
         BluetoothGattCharacteristic characteristic = getCharacteristic();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadPhyAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadPhyAction.java
index 8461fe8e1c..c10d5f78b8 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadPhyAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/ReadPhyAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2025 Thomas Kuehne
+/*  Copyright (C) 2025-2026 Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -21,6 +21,7 @@ import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothGatt;
 import android.os.Build;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 
 import org.slf4j.Logger;
@@ -47,7 +48,7 @@ public class ReadPhyAction extends BtLEAction {
 
     @SuppressLint("MissingPermission")
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         try {
             gatt.readPhy();
             return true;
@@ -57,6 +58,7 @@ public class ReadPhyAction extends BtLEAction {
         }
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName();
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestConnectionPriorityAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestConnectionPriorityAction.java
index d9a1a7f37e..229ba372db 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestConnectionPriorityAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestConnectionPriorityAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2023-2024 José Rebelo
+/*  Copyright (C) 2023-2026 José Rebelo
 
     This file is part of Gadgetbridge.
 
@@ -19,6 +19,8 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothGatt;
 
+import androidx.annotation.NonNull;
+
 import nodomain.freeyourgadget.gadgetbridge.service.btle.BleNamesResolver;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEAction;
 
@@ -38,10 +40,11 @@ public class RequestConnectionPriorityAction extends BtLEAction {
 
     @Override
     @SuppressLint("MissingPermission")
-    public boolean run(final BluetoothGatt gatt) {
+    public boolean run(@NonNull final BluetoothGatt gatt) {
         return gatt.requestConnectionPriority(priority);
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + " " +
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestMtuAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestMtuAction.java
index bc30a6576b..ffdbd9d58e 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestMtuAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/RequestMtuAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2019-2024 Andreas Shimokawa, Daniel Dakhno
+/*  Copyright (C) 2019-2026 Andreas Shimokawa, Daniel Dakhno
 
     This file is part of Gadgetbridge.
 
@@ -19,6 +19,9 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothGatt;
 
+import androidx.annotation.IntRange;
+import androidx.annotation.NonNull;
+
 import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEAction;
 import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCallback;
 
@@ -27,7 +30,7 @@ import nodomain.freeyourgadget.gadgetbridge.service.btle.GattCallback;
 public class RequestMtuAction extends BtLEAction {
     private final int mtu;
 
-    public RequestMtuAction(int mtu) {
+    public RequestMtuAction(@IntRange(from = 23L, to = 517L) final int mtu) {
         super(null);
         this.mtu = mtu;
     }
@@ -40,10 +43,11 @@ public class RequestMtuAction extends BtLEAction {
 
     @SuppressLint("MissingPermission")
     @Override
-    public boolean run(BluetoothGatt gatt) {
-        return gatt.requestMtu(this.mtu);
+    public boolean run(@NonNull final BluetoothGatt gatt) {
+        return gatt.requestMtu(mtu);
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + " mtu=" + mtu;
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceBusyAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceBusyAction.java
index 1d141df7a3..71345afaf8 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceBusyAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceBusyAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2025 Carsten Pfeiffer, Thomas Kuehne
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -45,7 +45,7 @@ public class SetDeviceBusyAction extends PlainAction {
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         if (busyTask == 0) {
             device.unsetBusyTask();
         } else {
@@ -56,6 +56,7 @@ public class SetDeviceBusyAction extends PlainAction {
         return true;
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getName() + " "
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceStateAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceStateAction.java
index 17eb53280b..da6e0dcf2b 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceStateAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetDeviceStateAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2025 Andreas Shimokawa, Carsten Pfeiffer, Daniel Dakhno, Thomas Kuehne
+/*  Copyright (C) 2015-2026 Andreas Shimokawa, Carsten Pfeiffer, Daniel Dakhno, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -28,18 +28,19 @@ public class SetDeviceStateAction extends PlainAction {
     private final GBDevice.State deviceState;
     private final Context context;
 
-    public SetDeviceStateAction(GBDevice device, GBDevice.State deviceState, Context context) {
+    public SetDeviceStateAction(@NonNull GBDevice device, @NonNull GBDevice.State deviceState, @NonNull Context context) {
         this.device = device;
         this.deviceState = deviceState;
         this.context = context;
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         device.setUpdateState(deviceState, context);
         return true;
     }
 
+    @NonNull
     public Context getContext() {
         return context;
     }
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetPreferredPhyAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetPreferredPhyAction.java
index a4e184f54c..cb142e4090 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetPreferredPhyAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetPreferredPhyAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2025 Thomas Kuehne
+/*  Copyright (C) 2025-2026 Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -21,6 +21,7 @@ import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothGatt;
 import android.os.Build;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.RequiresApi;
 
 import org.slf4j.Logger;
@@ -41,7 +42,7 @@ public class SetPreferredPhyAction extends BtLEAction {
     private final int mRxPhy;
     private final int mPhyOptions;
 
-    public SetPreferredPhyAction(int txPhy, int rxPhy, int phyOptions) {
+    public SetPreferredPhyAction(final int txPhy, final int rxPhy, final int phyOptions) {
         super(null);
         mTxPhy = txPhy;
         mRxPhy = rxPhy;
@@ -57,7 +58,7 @@ public class SetPreferredPhyAction extends BtLEAction {
 
     @SuppressLint("MissingPermission")
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull final BluetoothGatt gatt) {
         try {
             gatt.setPreferredPhy(mTxPhy, mRxPhy, mPhyOptions);
             return true;
@@ -68,6 +69,7 @@ public class SetPreferredPhyAction extends BtLEAction {
         }
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + " tx=" + mTxPhy
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetProgressAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetProgressAction.java
index 0bb75c3d4e..3254e974a3 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetProgressAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SetProgressAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2025 Andreas Shimokawa, Carsten Pfeiffer, José Rebelo, Thomas Kuehne
+/*  Copyright (C) 2015-2026 Andreas Shimokawa, Carsten Pfeiffer, José Rebelo, Thomas Kuehne
 
     This file is part of Gadgetbridge.
 
@@ -20,6 +20,7 @@ import android.bluetooth.BluetoothGatt;
 import android.content.Context;
 import android.content.Intent;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.StringRes;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
@@ -40,15 +41,15 @@ public class SetProgressAction extends PlainAction {
      * @param percentage Current percentage indicating how far along the action has progressed
      * @param context Context in which to create the notification
      */
-    public SetProgressAction(@StringRes int textRes, boolean ongoing, int percentage, Context context) {
-        this.text = context.getString(textRes);;
+    public SetProgressAction(@StringRes int textRes, boolean ongoing, int percentage, @NonNull Context context) {
+        this.text = context.getString(textRes);
         this.ongoing = ongoing;
         this.percentage = percentage;
         this.context = context;
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         GB.updateInstallNotification(this.text, this.ongoing, this.percentage, this.context);
 
         final LocalBroadcastManager broadcastManager = LocalBroadcastManager.getInstance(context);
@@ -63,6 +64,7 @@ public class SetProgressAction extends PlainAction {
         return true;
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + ": " + text + "; " + percentage + "%";
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SleepAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SleepAction.java
index 67afa4d20d..2eac56f6d5 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SleepAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/SleepAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2024 Carsten Pfeiffer
+/*  Copyright (C) 2015-2026 Carsten Pfeiffer
 
     This file is part of Gadgetbridge.
 
@@ -18,6 +18,9 @@ package nodomain.freeyourgadget.gadgetbridge.service.btle.actions;
 
 import android.bluetooth.BluetoothGatt;
 
+import androidx.annotation.IntRange;
+import androidx.annotation.NonNull;
+
 /**
  * An action that will cause the queue to {@link Thread#sleep(long) sleep} for the specified time.
  * Note that this is usually a bad idea, since it will not be able to process messages
@@ -25,22 +28,23 @@ import android.bluetooth.BluetoothGatt;
  */
 public class SleepAction extends PlainAction {
 
-    private final int mMillis;
+    private final long mMillis;
 
-    public SleepAction(int millis) {
+    public SleepAction(@IntRange(from = 0L) final long millis) {
         mMillis = millis;
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull final BluetoothGatt gatt) {
         try {
             Thread.sleep(mMillis);
             return true;
-        } catch (InterruptedException e) {
+        } catch (final InterruptedException e) {
             return false;
         }
     }
 
+    @NonNull
     @Override
     public String toString() {
         return getCreationTime() + " " + getClass().getSimpleName() + " " + mMillis + " ms";
diff --git a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/WriteAction.java b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/WriteAction.java
index eb24e9ec70..931a6fc80f 100644
--- a/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/WriteAction.java
+++ b/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/btle/actions/WriteAction.java
@@ -1,4 +1,4 @@
-/*  Copyright (C) 2015-2025 Andreas Shimokawa, Carsten Pfeiffer, Daniele
+/*  Copyright (C) 2015-2026 Andreas Shimokawa, Carsten Pfeiffer, Daniele
     Gobbetti, José Rebelo, Uwe Hermann, Thomas Kuehne
 
     This file is part of Gadgetbridge.
@@ -22,6 +22,8 @@ import android.bluetooth.BluetoothGatt;
 import android.bluetooth.BluetoothGattCharacteristic;
 import android.bluetooth.BluetoothStatusCodes;
 
+import androidx.annotation.NonNull;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -42,18 +44,18 @@ public class WriteAction extends BtLEAction {
     private final byte[] value;
     private final boolean legacyCompat;
 
-    public WriteAction(BluetoothGattCharacteristic characteristic, byte[] value) {
+    public WriteAction(@NonNull BluetoothGattCharacteristic characteristic, @NonNull byte[] value) {
         this(characteristic, value, false);
     }
 
-    public WriteAction(BluetoothGattCharacteristic characteristic, byte[] value, boolean legacyCompat) {
+    public WriteAction(@NonNull BluetoothGattCharacteristic characteristic, @NonNull byte[] value, boolean legacyCompat) {
         super(characteristic);
         this.value = value;
         this.legacyCompat = legacyCompat;
     }
 
     @Override
-    public boolean run(BluetoothGatt gatt) {
+    public boolean run(@NonNull BluetoothGatt gatt) {
         BluetoothGattCharacteristic characteristic = getCharacteristic();
         int properties = characteristic.getProperties();
         //TODO: expectsResult should return false if PROPERTY_WRITE_NO_RESPONSE is true, but this leads to timing issues
@@ -74,7 +76,7 @@ public class WriteAction extends BtLEAction {
     }
 
     @SuppressLint("MissingPermission")
-    private static boolean writeCharacteristicImp(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, byte[] value, boolean legacyCompat) {
+    private static boolean writeCharacteristicImp(@NonNull BluetoothGatt gatt, @NonNull BluetoothGattCharacteristic characteristic, @NonNull byte[] value, boolean legacyCompat) {
         if (GBApplication.isRunningTiramisuOrLater() && !legacyCompat) {
             // use API introduced in SDK level 33 to catch exceptions and more specific errors
             try {
@@ -109,6 +111,7 @@ public class WriteAction extends BtLEAction {
         return true;
     }
 
+    @NonNull
     @Override
     public String toString() {
         BluetoothGattCharacteristic characteristic = getCharacteristic();