Fix handling of nil interface parameters being passed to Do funcs.

gomock/call.go

@@ -203,7 +203,12 @@ func (c *Call) call(args []interface{}) (rets []interface{}, action func()) {
 		doArgs := make([]reflect.Value, len(args))
 		ft := c.doFunc.Type()
 		for i := 0; i < ft.NumIn(); i++ {
-			doArgs[i] = reflect.ValueOf(args[i])
+			if args[i] != nil {
+				doArgs[i] = reflect.ValueOf(args[i])
+			} else {
+				// Use the zero value for the arg.
+				doArgs[i] = reflect.Zero(ft.In(i))
+			}
 		}
 		action = func() { c.doFunc.Call(doArgs) }
 	}

sample/user_test.go

@@ -52,6 +52,15 @@ func TestRemember(t *testing.T) {
 	if calledString != "blah" {
 		t.Fatalf(`Uh oh. %q != "blah"`, calledString)
 	}
+
+	// Use Do with a nil arg.
+	mockIndex.EXPECT().Put("nil-key", gomock.Any()).Do(func(key string, value interface{}) {
+		if value != nil {
+			t.Errorf("Put did not pass through nil; got %v", value)
+		}
+	})
+	mockIndex.EXPECT().NillableRet()
+	user.Remember(mockIndex, []string{"nil-key"}, []interface{}{nil})
 }
 
 func TestGrabPointer(t *testing.T) {