diff --git a/EasyMapping/EKMapper.m b/EasyMapping/EKMapper.m
index e84c5af..d746f20 100644
--- a/EasyMapping/EKMapper.m
+++ b/EasyMapping/EKMapper.m
@@ -31,6 +31,15 @@ @implementation EKMapper
 
 + (id)objectFromExternalRepresentation:(NSDictionary *)externalRepresentation withMapping:(EKObjectMapping *)mapping
 {
+    NSParameterAssert([externalRepresentation isKindOfClass:[NSDictionary class]]);
+    NSParameterAssert([mapping isKindOfClass:[EKObjectMapping class]]);
+    
+    if (![externalRepresentation isKindOfClass:[NSDictionary class]] ||
+                ![mapping isKindOfClass:[EKObjectMapping class]])
+    {
+        return nil;
+    }
+    
     id object = [[mapping.objectClass alloc] init];
     return [self fillObject:object fromExternalRepresentation:externalRepresentation withMapping:mapping];
 }
@@ -76,6 +85,11 @@ + (NSArray *)arrayOfObjectsFromExternalRepresentation:(NSArray *)externalReprese
     NSParameterAssert([externalRepresentation isKindOfClass:[NSArray class]]);
     NSParameterAssert([mapping isKindOfClass:[EKObjectMapping class]]);
     
+    if (![externalRepresentation isKindOfClass:[NSArray class]] ||
+        ![mapping isKindOfClass:[EKObjectMapping class]]) {
+        return nil;
+    }
+    
     NSMutableArray *array = [NSMutableArray array];
     for (NSDictionary *representation in externalRepresentation) {
         id parsedObject = [self objectFromExternalRepresentation:representation withMapping:mapping];
diff --git a/EasyMapping/EKPropertyHelper.m b/EasyMapping/EKPropertyHelper.m
index c3630e5..5b4eb4e 100644
--- a/EasyMapping/EKPropertyHelper.m
+++ b/EasyMapping/EKPropertyHelper.m
@@ -64,6 +64,11 @@ + (NSString *) propertyTypeStringRepresentationFromProperty:(objc_property_t)pro
 
 + (id)propertyRepresentation:(NSArray *)array forObject:(id)object withPropertyName:(NSString *)propertyName
 {
+    if  (!array)
+    {
+        return nil;
+    }
+    
     objc_property_t property = class_getProperty([object class], [propertyName UTF8String]);
 	if (property)
     {