Update Observable.isInternalImplementation, get rid of NullPointerException

NullPointerException has been encountered during my tests. It is because java.lang.Class.getPackage() may return null "... if no package information is available from the archive or codebase" (documented feature).

Author: nj4x

rxjava-core/src/main/java/rx/Observable.java

@@ -3745,7 +3745,8 @@ private boolean isInternalImplementation(Object o) {
         if (o instanceof AtomicObserver)
             return true;
         // we treat the following package as "internal" and don't wrap it
-        return o.getClass().getPackage().getName().startsWith("rx.operators");
+        Package p = o.getClass().getPackage(); // it can be null
+        return p != null && p.getName().startsWith("rx.operators");
     }
 
     public static class UnitTest {