2 files changed, 20 insertions, 4 deletions
diff --git a/Framework/MASDictionaryTransformer.m b/Framework/MASDictionaryTransformer.m
index f0d9b2e..54a7d7a 100644
--- a/Framework/MASDictionaryTransformer.m
+++ b/Framework/MASDictionaryTransformer.m
@@ -11,12 +11,19 @@ static NSString *const MASModifierFlagsKey = @"modifierFlags";
     return YES;
 }
 
+// Storing nil values as an empty dictionary lets us differ between
+// “not available, use default value” and “explicitly set to none”.
+// See http://stackoverflow.com/questions/5540760 for details.
 - (NSDictionary*) reverseTransformedValue: (MASShortcut*) shortcut
 {
-    return @{
-        MASKeyCodeKey: @([shortcut keyCode]),
-        MASModifierFlagsKey: @([shortcut modifierFlags])
-    };
+    if (shortcut == nil) {
+        return [NSDictionary dictionary];
+    } else {
+        return @{
+            MASKeyCodeKey: @([shortcut keyCode]),
+            MASModifierFlagsKey: @([shortcut modifierFlags])
+        };
+    }
 }
 
 - (MASShortcut*) transformedValue: (NSDictionary*) dictionary
diff --git a/Framework/MASDictionaryTransformerTests.m b/Framework/MASDictionaryTransformerTests.m
index bd5c1db..48e11f3 100644
--- a/Framework/MASDictionaryTransformerTests.m
+++ b/Framework/MASDictionaryTransformerTests.m
@@ -20,4 +20,13 @@
         @"Decoding a shortcut from an incomplete dictionary returns nil.");
 }
 
+- (void) testNilRepresentation
+{
+    MASDictionaryTransformer *transformer = [MASDictionaryTransformer new];
+    XCTAssertEqualObjects([transformer reverseTransformedValue:nil], [NSDictionary dictionary],
+        @"Store nil values as an empty dictionary.");
+    XCTAssertNil([transformer transformedValue:[NSDictionary dictionary]],
+        @"Load empty dictionary as nil.");
+}
+
 @end