diff --git a/FastEasyMapping/Source/Cache/FEMObjectCache.h b/FastEasyMapping/Source/Cache/FEMObjectCache.h
index d7e0868..7967557 100644
--- a/FastEasyMapping/Source/Cache/FEMObjectCache.h
+++ b/FastEasyMapping/Source/Cache/FEMObjectCache.h
@@ -10,10 +10,7 @@ typedef _Nonnull id<NSFastEnumeration> (^FEMObjectCacheSource)(FEMMapping *mappi
 
 @interface FEMObjectCache : NSObject
 
-- (instancetype)init NS_UNAVAILABLE;
-+ (instancetype)new NS_UNAVAILABLE;
-
-- (instancetype)initWithSource:(FEMObjectCacheSource)source NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithSource:(nullable FEMObjectCacheSource)source NS_DESIGNATED_INITIALIZER;
 
 - (nullable id)objectForKey:(id)key mapping:(FEMMapping *)mapping;
 - (void)setObject:(id)object forKey:(id)key mapping:(FEMMapping *)mapping;
diff --git a/FastEasyMapping/Source/Cache/FEMObjectCache.m b/FastEasyMapping/Source/Cache/FEMObjectCache.m
index 50c1d59..7b7eb92 100644
--- a/FastEasyMapping/Source/Cache/FEMObjectCache.m
+++ b/FastEasyMapping/Source/Cache/FEMObjectCache.m
@@ -7,6 +7,10 @@
 #import "FEMMapping.h"
 #import "FEMRepresentationUtility.h"
 
+FEMObjectCacheSource FEMObjectCacheSourceStub = ^id<NSFastEnumeration> (FEMMapping *mapping) {
+    return @[];
+};
+
 @implementation FEMObjectCache {
 	NSMapTable<FEMMapping *, NSMutableDictionary<id, id> *> *_lookupObjectsMap;
 	FEMObjectCacheSource _source;
@@ -15,10 +19,9 @@ @implementation FEMObjectCache {
 #pragma mark - Init
 
 - (instancetype)initWithSource:(FEMObjectCacheSource)source {
-	NSParameterAssert(source != NULL);
 	self = [super init];
 	if (self) {
-		_source = [source copy];
+        _source = source ?: FEMObjectCacheSourceStub;
 
         NSPointerFunctionsOptions options = NSPointerFunctionsObjectPointerPersonality | NSPointerFunctionsStrongMemory;
 		_lookupObjectsMap = [[NSMapTable alloc] initWithKeyOptions:options valueOptions:options capacity:0];
@@ -27,6 +30,10 @@ - (instancetype)initWithSource:(FEMObjectCacheSource)source {
 	return self;
 }
 
+- (instancetype)init {
+    return [self initWithSource:nil];
+}
+
 #pragma mark - Inspection
 
 - (NSMutableDictionary *)fetchExistingObjectsForMapping:(FEMMapping *)mapping {
diff --git a/FastEasyMappingTests/Specs/FEMCacheSpec.m b/FastEasyMappingTests/Specs/FEMCacheSpec.m
index bd6fd6d..fa4fd06 100644
--- a/FastEasyMappingTests/Specs/FEMCacheSpec.m
+++ b/FastEasyMappingTests/Specs/FEMCacheSpec.m
@@ -132,4 +132,34 @@
         });
     });
 
+    describe(@"indirect relationship", ^{
+        __block FEMMapping *mappingA;
+        __block FEMMapping *mappingB;
+        __block FEMObjectCache *cache;
+        
+        beforeEach(^{
+            mappingA = [[FEMMapping alloc] initWithObjectClass:[NSObject class]];
+            mappingA.primaryKey = @"a";
+            
+            mappingB = [[FEMMapping alloc] initWithObjectClass:[NSObject class]];
+            mappingB.primaryKey = @"b";
+            
+            cache = [[FEMObjectCache alloc] init];
+        });
+        
+        it(@"should combine objects from similar mappings", ^{
+            NSObject *a = [NSObject new];
+            NSObject *b = [NSObject new];
+            
+            [cache setObject:a forKey:@1 mapping:mappingA];
+            [cache setObject:b forKey:@2 mapping:mappingB];
+            
+            [[[cache objectForKey:@1 mapping:mappingA] should] equal:a];
+            [[[cache objectForKey:@1 mapping:mappingB] should] equal:a];
+            
+            [[[cache objectForKey:@2 mapping:mappingA] should] equal:b];
+            [[[cache objectForKey:@2 mapping:mappingB] should] equal:b];
+        });
+    });
+
 SPEC_END