Fixed build by updating android gradle plugin version.

Infer nullability annotation.

Author: ESinyak

bolts-applinks/build.gradle

@@ -28,7 +28,7 @@ dependencies {
 
     testCompile 'junit:junit:4.12'
 
-    androidTestCompile 'com.android.support:support-v4:23.0.1'
+    androidTestCompile 'com.android.support:support-v4:28.0.0'
 }
 
 android.libraryVariants.all { variant ->

bolts-tasks/build.gradle

@@ -9,7 +9,6 @@ configurations {
 
 android {
     compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
 
     defaultConfig {
         minSdkVersion rootProject.ext.minSdkVersion
@@ -24,6 +23,7 @@ sourceSets {
 
 dependencies {
     testCompile 'junit:junit:4.12'
+    implementation 'com.android.support:support-annotations:28.0.0'
 }
 
 //region Maven

bolts-tasks/src/main/java/com/anchorfree/bolts/AggregateException.java

@@ -9,6 +9,8 @@
  */
 package com.anchorfree.bolts;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import java.io.PrintStream;
 import java.io.PrintWriter;
 import java.util.ArrayList;
@@ -51,7 +53,7 @@ public AggregateException(String detailMessage, Throwable[] innerThrowables) {
    * @param innerThrowables
    *            The exceptions that are the cause of the current exception.
    */
-  public AggregateException(String detailMessage, List<? extends Throwable> innerThrowables) {
+  public AggregateException(String detailMessage, @Nullable List<? extends Throwable> innerThrowables) {
     super(detailMessage,
         innerThrowables != null && innerThrowables.size() > 0 ? innerThrowables.get(0) : null);
     this.innerThrowables = Collections.unmodifiableList(innerThrowables);
@@ -77,7 +79,7 @@ public List<Throwable> getInnerThrowables() {
   }
 
   @Override
-  public void printStackTrace(PrintStream err) {
+  public void printStackTrace(@NonNull PrintStream err) {
     super.printStackTrace(err);
 
     int currentIndex = -1;
@@ -92,7 +94,7 @@ public void printStackTrace(PrintStream err) {
   }
 
   @Override
-  public void printStackTrace(PrintWriter err) {
+  public void printStackTrace(@NonNull PrintWriter err) {
     super.printStackTrace(err);
 
     int currentIndex = -1;
@@ -109,6 +111,7 @@ public void printStackTrace(PrintWriter err) {
   /**
    * @deprecated Please use {@link #getInnerThrowables()} instead.
    */
+  @NonNull
   @Deprecated
   public List<Exception> getErrors() {
     List<Exception> errors = new ArrayList<Exception>();

bolts-tasks/src/main/java/com/anchorfree/bolts/AndroidExecutors.java

@@ -14,6 +14,7 @@
 import android.os.Handler;
 import android.os.Looper;
 
+import android.support.annotation.NonNull;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.LinkedBlockingQueue;
@@ -39,7 +40,7 @@
 
   private static final AndroidExecutors INSTANCE = new AndroidExecutors();
 
-  private final Executor uiThread;
+  @NonNull private final Executor uiThread;
 
   private AndroidExecutors() {
     uiThread = new UIThreadExecutor();
@@ -70,6 +71,7 @@ private AndroidExecutors() {
    *
    * @return the newly created thread pool
    */
+  @NonNull
   public static ExecutorService newCachedThreadPool() {
     ThreadPoolExecutor executor =  new ThreadPoolExecutor(
         CORE_POOL_SIZE,
@@ -93,6 +95,7 @@ public static ExecutorService newCachedThreadPool() {
    * @param threadFactory the factory to use when creating new threads
    * @return the newly created thread pool
    */
+  @NonNull
   public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
     ThreadPoolExecutor executor =  new ThreadPoolExecutor(
             CORE_POOL_SIZE,
@@ -116,7 +119,7 @@ public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
    * @param value true if should time out, else false
    */
   @SuppressLint("NewApi")
-  public static void allowCoreThreadTimeout(ThreadPoolExecutor executor, boolean value) {
+  public static void allowCoreThreadTimeout(@NonNull ThreadPoolExecutor executor, boolean value) {
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD) {
       executor.allowCoreThreadTimeOut(value);
     }
@@ -125,6 +128,7 @@ public static void allowCoreThreadTimeout(ThreadPoolExecutor executor, boolean v
   /**
    * An {@link java.util.concurrent.Executor} that executes tasks on the UI thread.
    */
+  @NonNull
   public static Executor uiThread() {
     return INSTANCE.uiThread;
   }

bolts-tasks/src/main/java/com/anchorfree/bolts/BoltsExecutors.java

@@ -1,5 +1,6 @@
 package com.anchorfree.bolts;
 
+import android.support.annotation.NonNull;
 import java.util.Locale;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
@@ -21,9 +22,9 @@ private static boolean isAndroidRuntime() {
     return javaRuntimeName.toLowerCase(Locale.US).contains("android");
   }
 
-  private final ExecutorService background;
+  @NonNull private final ExecutorService background;
   private final ScheduledExecutorService scheduled;
-  private final Executor immediate;
+  @NonNull private final Executor immediate;
 
   private BoltsExecutors() {
     background = !isAndroidRuntime()
@@ -36,6 +37,7 @@ private BoltsExecutors() {
   /**
    * An {@link java.util.concurrent.Executor} that executes tasks in parallel.
    */
+  @NonNull
   public static ExecutorService background() {
     return INSTANCE.background;
   }
@@ -49,7 +51,8 @@ public static ExecutorService background() {
    * the stack runs too deep, at which point it will delegate to {@link BoltsExecutors#background}
    * in order to trim the stack.
    */
-  /* package */ static Executor immediate() {
+  /* package */ @NonNull
+  static Executor immediate() {
     return INSTANCE.immediate;
   }
 
@@ -61,7 +64,7 @@ public static ExecutorService background() {
    */
   private static class ImmediateExecutor implements Executor {
     private static final int MAX_DEPTH = 15;
-    private ThreadLocal<Integer> executionDepth = new ThreadLocal<>();
+    @NonNull private ThreadLocal<Integer> executionDepth = new ThreadLocal<>();
 
     /**
      * Increments the depth.
@@ -98,7 +101,7 @@ private int decrementDepth() {
     }
 
     @Override
-    public void execute(Runnable command) {
+    public void execute(@NonNull Runnable command) {
       int depth = incrementDepth();
       try {
         if (depth <= MAX_DEPTH) {

bolts-tasks/src/main/java/com/anchorfree/bolts/CancellationToken.java

@@ -9,6 +9,7 @@
  */
 package com.anchorfree.bolts;
 
+import android.support.annotation.NonNull;
 import java.util.Locale;
 import java.util.concurrent.CancellationException;
 
@@ -61,6 +62,7 @@ public void throwIfCancellationRequested() throws CancellationException {
     tokenSource.throwIfCancellationRequested();
   }
 
+  @NonNull
   @Override
   public String toString() {
     return String.format(Locale.US, "%s@%s[cancellationRequested=%s]",

bolts-tasks/src/main/java/com/anchorfree/bolts/CancellationTokenRegistration.java

@@ -9,6 +9,7 @@
  */
 package com.anchorfree.bolts;
 
+import android.support.annotation.Nullable;
 import java.io.Closeable;
 
 /**
@@ -19,8 +20,8 @@
 public class CancellationTokenRegistration implements Closeable {
 
   private final Object lock = new Object();
-  private CancellationTokenSource tokenSource;
-  private Runnable action;
+  @Nullable private CancellationTokenSource tokenSource;
+  @Nullable private Runnable action;
   private boolean closed;
 
   /* package */ CancellationTokenRegistration(CancellationTokenSource tokenSource, Runnable action) {

bolts-tasks/src/main/java/com/anchorfree/bolts/CancellationTokenSource.java

@@ -9,6 +9,8 @@
  */
 package com.anchorfree.bolts;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import java.io.Closeable;
 import java.util.ArrayList;
 import java.util.List;
@@ -31,7 +33,7 @@ public class CancellationTokenSource implements Closeable {
   private final Object lock = new Object();
   private final List<CancellationTokenRegistration> registrations = new ArrayList<>();
   private final ScheduledExecutorService executor = BoltsExecutors.scheduled();
-  private ScheduledFuture<?> scheduledCancellation;
+  @Nullable private ScheduledFuture<?> scheduledCancellation;
   private boolean cancellationRequested;
   private boolean closed;
 
@@ -54,6 +56,7 @@ public boolean isCancellationRequested() {
   /**
    * @return the token that can be passed to asynchronous method to control cancellation.
    */
+  @NonNull
   public CancellationToken getToken() {
     synchronized (lock) {
       throwIfClosed();
@@ -184,6 +187,7 @@ private void notifyListeners(List<CancellationTokenRegistration> registrations)
     }
   }
 
+  @NonNull
   @Override
   public String toString() {
     return String.format(Locale.US, "%s@%s[cancellationRequested=%s]",

bolts-tasks/src/main/java/com/anchorfree/bolts/Continuation.java

@@ -9,6 +9,8 @@
  */
 package com.anchorfree.bolts;
 
+import android.support.annotation.Nullable;
+
 /**
  * A function to be called after a task completes.
  *
@@ -18,5 +20,6 @@
  * @see Task
  */
 public interface Continuation<TTaskResult, TContinuationResult> {
+  @Nullable
   TContinuationResult then(Task<TTaskResult> task) throws Exception;
 }