2.x: Delegate null Collections down to onError in toList (#4731)

Author: vanniktech

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.internal.functions.ObjectHelper;
 import java.util.Collection;
 import java.util.concurrent.Callable;
 
@@ -33,7 +34,7 @@ public FlowableToList(Publisher<T> source, Callable<U> collectionSupplier) {
     protected void subscribeActual(Subscriber<? super U> s) {
         U coll;
         try {
-            coll = collectionSupplier.call();
+            coll = ObjectHelper.requireNonNull(collectionSupplier.call(), "The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
         } catch (Throwable e) {
             Exceptions.throwIfFatal(e);
             EmptySubscription.error(e, s);

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.internal.functions.ObjectHelper;
 import java.util.Collection;
 import java.util.concurrent.Callable;
 
@@ -47,7 +48,7 @@ public FlowableToListSingle(Publisher<T> source, Callable<U> collectionSupplier)
     protected void subscribeActual(SingleObserver<? super U> s) {
         U coll;
         try {
-            coll = collectionSupplier.call();
+            coll = ObjectHelper.requireNonNull(collectionSupplier.call(), "The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
         } catch (Throwable e) {
             Exceptions.throwIfFatal(e);
             EmptyDisposable.error(e, s);

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

@@ -42,7 +42,7 @@ public ObservableToList(ObservableSource<T> source, Callable<U> collectionSuppli
     public void subscribeActual(Observer<? super U> t) {
         U coll;
         try {
-            coll = ObjectHelper.requireNonNull(collectionSupplier.call(), "The collectionSupplier returned a null Collection");
+            coll = ObjectHelper.requireNonNull(collectionSupplier.call(), "The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
         } catch (Throwable e) {
             Exceptions.throwIfFatal(e);
             EmptyDisposable.error(e, t);

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.observable;
 
+import io.reactivex.internal.functions.ObjectHelper;
 import java.util.*;
 import java.util.concurrent.Callable;
 
@@ -48,7 +49,7 @@ public ObservableToListSingle(ObservableSource<T> source, Callable<U> collection
     public void subscribeActual(SingleObserver<? super U> t) {
         U coll;
         try {
-            coll = collectionSupplier.call();
+            coll = ObjectHelper.requireNonNull(collectionSupplier.call(), "The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
         } catch (Throwable e) {
             Exceptions.throwIfFatal(e);
             EmptyDisposable.error(e, t);

src/test/java/io/reactivex/internal/operators/flowable/FlowableToListTest.java

@@ -345,6 +345,22 @@ public Collection<Integer> call() throws Exception {
         .assertFailure(TestException.class);
     }
 
+    @SuppressWarnings("unchecked")
+    @Test
+    public void collectionSupplierReturnsNull() {
+        Flowable.just(1)
+        .toList(new Callable<Collection<Integer>>() {
+            @Override
+            public Collection<Integer> call() throws Exception {
+                return null;
+            }
+        })
+        .toFlowable()
+        .test()
+        .assertFailure(NullPointerException.class)
+        .assertErrorMessage("The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     public void singleCollectionSupplierThrows() {
@@ -358,4 +374,19 @@ public Collection<Integer> call() throws Exception {
         .test()
         .assertFailure(TestException.class);
     }
-}
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void singleCollectionSupplierReturnsNull() {
+        Flowable.just(1)
+        .toList(new Callable<Collection<Integer>>() {
+            @Override
+            public Collection<Integer> call() throws Exception {
+                return null;
+            }
+        })
+        .test()
+        .assertFailure(NullPointerException.class)
+        .assertErrorMessage("The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
+    }
+}

src/test/java/io/reactivex/internal/operators/observable/ObservableToListTest.java

@@ -226,6 +226,22 @@ public Collection<Integer> call() throws Exception {
         .assertFailure(TestException.class);
     }
 
+    @SuppressWarnings("unchecked")
+    @Test
+    public void collectionSupplierReturnsNull() {
+        Observable.just(1)
+        .toList(new Callable<Collection<Integer>>() {
+            @Override
+            public Collection<Integer> call() throws Exception {
+                return null;
+            }
+        })
+        .toObservable()
+        .test()
+        .assertFailure(NullPointerException.class)
+        .assertErrorMessage("The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     public void singleCollectionSupplierThrows() {
@@ -239,4 +255,19 @@ public Collection<Integer> call() throws Exception {
         .test()
         .assertFailure(TestException.class);
     }
-}
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void singleCollectionSupplierReturnsNull() {
+        Observable.just(1)
+        .toList(new Callable<Collection<Integer>>() {
+            @Override
+            public Collection<Integer> call() throws Exception {
+                return null;
+            }
+        })
+        .test()
+        .assertFailure(NullPointerException.class)
+        .assertErrorMessage("The collectionSupplier returned a null collection. Null values are generally not allowed in 2.x operators and sources.");
+    }
+}