add nullable annotation to simple queue (fixes #5053) (#5054)

Author: jschneider

src/main/java/io/reactivex/internal/disposables/EmptyDisposable.java

@@ -14,6 +14,7 @@
 package io.reactivex.internal.disposables;
 
 import io.reactivex.*;
+import io.reactivex.annotations.Nullable;
 import io.reactivex.internal.fuseable.QueueDisposable;
 
 /**
@@ -93,6 +94,7 @@ public boolean offer(Object v1, Object v2) {
         throw new UnsupportedOperationException("Should not be called!");
     }
 
+    @Nullable
     @Override
     public Object poll() throws Exception {
         return null; // always empty

src/main/java/io/reactivex/internal/fuseable/SimplePlainQueue.java

@@ -13,13 +13,16 @@
 
 package io.reactivex.internal.fuseable;
 
+import io.reactivex.annotations.Nullable;
+
 /**
  * Override of the SimpleQueue interface with no throws Exception on poll.
  *
  * @param <T> the value type to enqueue and dequeue, not null
  */
 public interface SimplePlainQueue<T> extends SimpleQueue<T> {
 
+    @Nullable
     @Override
     T poll();
 }

src/main/java/io/reactivex/internal/fuseable/SimpleQueue.java

@@ -13,6 +13,8 @@
 
 package io.reactivex.internal.fuseable;
 
+import io.reactivex.annotations.Nullable;
+
 /**
  * A minimalist queue interface without the method bloat of java.util.Collection and java.util.Queue.
  *
@@ -24,6 +26,10 @@ public interface SimpleQueue<T> {
 
     boolean offer(T v1, T v2);
 
+    /**
+     * @return null to indicate an empty queue
+     */
+    @Nullable
     T poll() throws Exception;
 
     boolean isEmpty();

src/main/java/io/reactivex/internal/observers/DeferredScalarDisposable.java

@@ -14,6 +14,7 @@
 package io.reactivex.internal.observers;
 
 import io.reactivex.Observer;
+import io.reactivex.annotations.Nullable;
 import io.reactivex.plugins.RxJavaPlugins;
 
 /**
@@ -110,6 +111,7 @@ public final void complete() {
         actual.onComplete();
     }
 
+    @Nullable
     @Override
     public final T poll() throws Exception {
         if (get() == FUSED_READY) {

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

@@ -16,6 +16,7 @@
 import java.util.Iterator;
 import java.util.concurrent.atomic.*;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.Flowable;
@@ -466,6 +467,7 @@ public int requestFusion(int requestedMode) {
             return m;
         }
 
+        @Nullable
         @SuppressWarnings("unchecked")
         @Override
         public R poll() throws Exception {

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

@@ -16,6 +16,7 @@
 import java.util.Collection;
 import java.util.concurrent.Callable;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.exceptions.Exceptions;
@@ -117,6 +118,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             for (;;) {

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.functions.*;
@@ -106,6 +107,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             for (;;) {
@@ -195,6 +197,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             for (;;) {

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.annotations.Experimental;
@@ -74,6 +75,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();
@@ -122,6 +124,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.annotations.Experimental;
@@ -130,6 +131,7 @@ public boolean isEmpty() {
             return qs.isEmpty();
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();
@@ -239,6 +241,7 @@ public boolean isEmpty() {
             return qs.isEmpty();
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();

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

@@ -13,6 +13,7 @@
 
 package io.reactivex.internal.operators.flowable;
 
+import io.reactivex.annotations.Nullable;
 import org.reactivestreams.*;
 
 import io.reactivex.exceptions.*;
@@ -144,6 +145,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();
@@ -276,6 +278,7 @@ public int requestFusion(int mode) {
             return transitiveBoundaryFusion(mode);
         }
 
+        @Nullable
         @Override
         public T poll() throws Exception {
             T v = qs.poll();