jni: Allow nullptr to be converted to JavaParamRef.

base/android/scoped_java_ref.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_ANDROID_SCOPED_JAVA_REF_H_
 #define BASE_ANDROID_SCOPED_JAVA_REF_H_
 
 #include <jni.h>
 #include <stddef.h>
 
@@ skipping 88 matching lines @@
 // Method parameters should not be deleted, and so this class exists purely to
 // wrap them as a JavaRef<T> in the JNI binding generator. Do not create
 // instances manually.
 template<typename T>
 class JavaParamRef : public JavaRef<T> {
  public:
   // Assumes that |obj| is a parameter passed to a JNI method from Java.
   // Does not assume ownership as parameters should not be deleted.
   JavaParamRef(JNIEnv* env, T obj) : JavaRef<T>(env, obj) {}
 
+  // Allow nullptr to be converted to JavaParamRef. Some unit tests call JNI
+  // methods directly from C++ and pass null for objects which are not actually
+  // used by the implementation (e.g. the caller object); allow this to keep
+  // working.
+  JavaParamRef(std::nullptr_t) : JavaRef<T>() {}
+
   ~JavaParamRef() {}
 
   // TODO(torne): remove this cast once we're using JavaRef consistently.
   // http://crbug.com/506850
   operator T() const { return JavaRef<T>::obj(); }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(JavaParamRef);
 };
 
@@ skipping 135 matching lines @@
   // is *not* a transfer of ownership and Release() should not be used.
   T Release() {
     return static_cast<T>(this->ReleaseInternal());
   }
 };
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_SCOPED_JAVA_REF_H_