2.x: Enhance NPE message in Create functions of all Base Reactive Types (#4561)

Author: vanniktech

src/main/java/io/reactivex/internal/operators/completable/CompletableCreate.java

@@ -74,7 +74,7 @@ public void onComplete() {
         @Override
         public void onError(Throwable t) {
             if (t == null) {
-                t = new NullPointerException();
+                t = new NullPointerException("Emitter got a null throwable. Null values are generally not allowed in 2.x operators and sources.");
             }
             if (get() != DisposableHelper.DISPOSED) {
                 Disposable d = getAndSet(DisposableHelper.DISPOSED);

src/main/java/io/reactivex/internal/operators/flowable/FlowableCreate.java

@@ -107,7 +107,7 @@ public void onNext(T t) {
                 return;
             }
             if (t == null) {
-                onError(new NullPointerException("t is null"));
+                onError(new NullPointerException("Emitter got a null value. Null values are generally not allowed in 2.x operators and sources."));
                 return;
             }
             if (get() == 0 && compareAndSet(0, 1)) {
@@ -134,7 +134,7 @@ public void onError(Throwable t) {
                 return;
             }
             if (t == null) {
-                t = new NullPointerException("t is null");
+                t = new NullPointerException("Emitter got a null throwable. Null values are generally not allowed in 2.x operators and sources.");
             }
             if (error.addThrowable(t)) {
                 done = true;

src/main/java/io/reactivex/internal/operators/maybe/MaybeCreate.java

@@ -69,7 +69,7 @@ public void onSuccess(T value) {
                 if (d != DisposableHelper.DISPOSED) {
                     try {
                         if (value == null) {
-                            actual.onError(new NullPointerException());
+                            actual.onError(new NullPointerException("Emitter got a null value. Null values are generally not allowed in 2.x operators and sources."));
                         } else {
                             actual.onSuccess(value);
                         }
@@ -85,7 +85,7 @@ public void onSuccess(T value) {
         @Override
         public void onError(Throwable t) {
             if (t == null) {
-                t = new NullPointerException();
+                t = new NullPointerException("Emitter got a null throwable. Null values are generally not allowed in 2.x operators and sources.");
             }
             if (get() != DisposableHelper.DISPOSED) {
                 Disposable d = getAndSet(DisposableHelper.DISPOSED);

src/main/java/io/reactivex/internal/operators/observable/ObservableCreate.java

@@ -60,7 +60,7 @@ static final class CreateEmitter<T>
         @Override
         public void onNext(T t) {
             if (t == null) {
-                onError(new NullPointerException());
+                onError(new NullPointerException("Emitter got a null value. Null values are generally not allowed in 2.x operators and sources."));
             }
             if (!isDisposed()) {
                 observer.onNext(t);
@@ -70,7 +70,7 @@ public void onNext(T t) {
         @Override
         public void onError(Throwable t) {
             if (t == null) {
-                t = new NullPointerException();
+                t = new NullPointerException("Emitter got a null throwable. Null values are generally not allowed in 2.x operators and sources.");
             }
             if (!isDisposed()) {
                 try {

src/main/java/io/reactivex/internal/operators/single/SingleCreate.java

@@ -63,7 +63,7 @@ public void onSuccess(T value) {
                 if (d != DisposableHelper.DISPOSED) {
                     try {
                         if (value == null) {
-                            actual.onError(new NullPointerException());
+                            actual.onError(new NullPointerException("Emitter got a null value. Null values are generally not allowed in 2.x operators and sources."));
                         } else {
                             actual.onSuccess(value);
                         }
@@ -79,7 +79,7 @@ public void onSuccess(T value) {
         @Override
         public void onError(Throwable t) {
             if (t == null) {
-                t = new NullPointerException();
+                t = new NullPointerException("Emitter got a null throwable. Null values are generally not allowed in 2.x operators and sources.");
             }
             if (get() != DisposableHelper.DISPOSED) {
                 Disposable d = getAndSet(DisposableHelper.DISPOSED);