Added specs around behavior of empty mappable payloads and RKObjectLoaderDelegate invocations. Fixed issue where empty hashes ({}) would result in no delegate methods being invoked. fixes #225

Code/ObjectMapping/RKObjectLoader.m

@@ -164,7 +164,7 @@
             return [RKObjectMappingResult mappingResultWithDictionary:[NSDictionary dictionaryWithObject:self.targetObject forKey:@""]];
         }
         
-        return nil;
+        return [RKObjectMappingResult mappingResultWithDictionary:[NSDictionary dictionary]];
     }
     
     id parsedData = [parser objectFromString:bodyAsString error:error];
@@ -223,15 +223,11 @@
     
     NSError* error = nil;
     _result = [[self performMapping:&error] retain];
+    NSAssert(_result || error, @"Expected performMapping to return a mapping result or an error.");
     if (self.result) {
         [self processMappingResult:self.result];
     } else if (error) {
         [self didFailLoadWithError:error];
-    } else {
-        // TODO: This is causing no didLoadObject: flavored delegate methods to be invoked.
-        
-        // A nil response with an error indicates success, but no mapping results
-        [self finalizeLoad:YES error:nil];
     }
 
 	[pool drain];

Code/ObjectMapping/RKObjectMapper.m

@@ -260,7 +260,9 @@
     }
     
     // If we found nothing eligible for mapping in the content, add an unmappable key path error and fail mapping
-    if (foundMappable == NO) {
+    // If the content is empty, we don't consider it an error
+    BOOL isEmpty = [self.sourceObject respondsToSelector:@selector(count)] && ([self.sourceObject count] == 0);
+    if (foundMappable == NO && !isEmpty) {
         [self addErrorForUnmappableKeyPath:@""];
         return nil;
     }

Specs/ObjectMapping/RKObjectLoaderSpec.m

@@ -431,4 +431,36 @@
     assertThatBool(responseLoader.success, is(equalToBool(YES)));
 }
 
+- (void)itShouldInvokeTheDelegateOnSuccessIfTheResponseIsAnEmptyArray {
+    RKObjectManager* objectManager = RKSpecNewObjectManager();    
+    RKSpecResponseLoader* responseLoader = [RKSpecResponseLoader responseLoader];
+    responseLoader.timeout = 20;
+    [objectManager loadObjectsAtResourcePath:@"/empty/array" delegate:responseLoader];
+    [responseLoader waitForResponse];
+    assertThat(responseLoader.objects, isNot(nilValue()));
+    assertThatBool([responseLoader.objects isKindOfClass:[NSArray class]], is(equalToBool(YES)));
+    assertThat(responseLoader.objects, is(empty()));
+}
+
+- (void)itShouldInvokeTheDelegateOnSuccessIfTheResponseIsAnEmptyDictionary {
+    RKObjectManager* objectManager = RKSpecNewObjectManager();    
+    RKSpecResponseLoader* responseLoader = [RKSpecResponseLoader responseLoader];
+    responseLoader.timeout = 20;
+    [objectManager loadObjectsAtResourcePath:@"/empty/dictionary" delegate:responseLoader];
+    [responseLoader waitForResponse];
+    assertThat(responseLoader.objects, isNot(nilValue()));
+    assertThatBool([responseLoader.objects isKindOfClass:[NSArray class]], is(equalToBool(YES)));
+    assertThat(responseLoader.objects, is(empty()));
+}
+
+- (void)itShouldInvokeTheDelegateOnSuccessIfTheResponseIsAnEmptyString {
+    RKObjectManager* objectManager = RKSpecNewObjectManager();    
+    RKSpecResponseLoader* responseLoader = [RKSpecResponseLoader responseLoader];
+    responseLoader.timeout = 20;
+    [objectManager loadObjectsAtResourcePath:@"/empty/string" delegate:responseLoader];
+    [responseLoader waitForResponse];
+    assertThat(responseLoader.objects, isNot(nilValue()));
+    assertThatBool([responseLoader.objects isKindOfClass:[NSArray class]], is(equalToBool(YES)));
+    assertThat(responseLoader.objects, is(empty()));
+}
 @end

Specs/Server/server.rb

@@ -101,6 +101,24 @@ class RestKit::SpecServer < Sinatra::Base
     params.to_json
   end
   
+  get '/empty/array' do
+    status 200
+    content_type 'application/json'
+    [].to_json
+  end
+  
+  get '/empty/dictionary' do
+    status 200
+    content_type 'application/json'
+    {}.to_json
+  end
+  
+  get '/empty/string' do
+    status 200
+    content_type 'application/json'
+    ""
+  end
+  
   # start the server if ruby file executed directly
   run! if app_file == $0
 end