2.x: RxJavaPlugins - Don't pass null throwable down to Error Handler (#4603)

Author: vanniktech

src/main/java/io/reactivex/plugins/RxJavaPlugins.java

@@ -252,23 +252,22 @@ public static Scheduler onComputationScheduler(Scheduler defaultScheduler) {
      */
     public static void onError(Throwable error) {
         Consumer<Throwable> f = errorHandler;
+
+        if (error == null) {
+            error = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
+        }
+
         if (f != null) {
             try {
                 f.accept(error);
                 return;
             } catch (Throwable e) {
                 // Exceptions.throwIfFatal(e); TODO decide
-                if (error == null) {
-                    error = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
-                }
                 e.printStackTrace(); // NOPMD
                 uncaught(e);
             }
-        } else {
-            if (error == null) {
-                error = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
-            }
         }
+
         error.printStackTrace(); // NOPMD
         uncaught(error);
     }

src/test/java/io/reactivex/plugins/RxJavaPluginsTest.java

@@ -16,6 +16,7 @@
 
 package io.reactivex.plugins;
 
+import java.util.concurrent.atomic.AtomicReference;
 import static org.junit.Assert.*;
 
 import java.io.IOException;
@@ -1695,4 +1696,25 @@ public void onComplete() {
         .assertComplete();
     }
 
-}
+    @Test
+    public void onErrorNull() {
+        try {
+            final AtomicReference<Throwable> t = new AtomicReference<Throwable>();
+
+            RxJavaPlugins.setErrorHandler(new Consumer<Throwable>() {
+                @Override
+                public void accept(final Throwable throwable) throws Exception {
+                    t.set(throwable);
+                }
+            });
+
+            RxJavaPlugins.onError(null);
+
+            final Throwable throwable = t.get();
+            assertEquals("onError called with null. Null values are generally not allowed in 2.x operators and sources.", throwable.getMessage());
+            assertTrue(throwable instanceof NullPointerException);
+        } finally {
+            RxJavaPlugins.reset();
+        }
+    }
+}