Map null callback objects to null pointers

libtest/ClosureTest.c

@@ -15,7 +15,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
+int testClosureNull(int (*closure)(void), int defaultValue)
+{
+    return closure ? (*closure)() : defaultValue;
+}
 void testClosureVrV(void (*closure)(void))
 {
     (*closure)();

src/main/java/jnr/ffi/provider/jffi/NativeClosureManager.java

@@ -91,6 +91,10 @@ private ClosureSite(NativeClosureFactory<T> factory) {
         }
 
         public Pointer toNative(T value, ToNativeContext context) {
+            if (value == null) {
+                return null;
+            }
+
             // If passing down a function pointer, don't re-wrap it
             if (value instanceof ClosureFromNativeConverter.AbstractClosurePointer) {
                 return (ClosureFromNativeConverter.AbstractClosurePointer) value;

src/test/java/jnr/ffi/DelegateTest.java

@@ -51,6 +51,10 @@ public void tearDown() {
     }
 
     public static interface TestLib {
+        public static interface CallableNull {
+            @Delegate public int call();
+        }
+        int testClosureNull(CallableNull closure, int defaultValue);
         public static interface CallableVrV {
             @Delegate public void call();
         }
@@ -151,6 +155,26 @@ public interface ReusableCallable {
         public CallableIrV ret_pointer(CallableIrV callable);
     }
     @Test
+    public void closureNullWithValue() {
+        final boolean[] called = { false };
+        final TestLib.CallableNull closure = new TestLib.CallableNull() {
+
+            public int call() {
+                called[0] = true;
+                return 42;
+            }
+        };
+        int retValue = lib.testClosureNull(closure, 41);
+        assertTrue("Callable not called", called[0]);
+        assertEquals("Incorrect return value from callable", 42, retValue);
+    }
+    @Test
+    public void closureNullWithNull() {
+        final TestLib.CallableNull closure = null;
+        int retValue = lib.testClosureNull(closure, 41);
+        assertEquals("Incorrect return value from callable", 41, retValue);
+    }
+    @Test
     public void closureVrV() {
         final boolean[] called = { false };
         final TestLib.CallableVrV closure = new TestLib.CallableVrV() {