-Fix crash

Pod/Classes/PNObject.m

@@ -208,9 +208,7 @@ NSString * const PNObjectMappingSelector = @"selector";
     NSString *mappedJSONType;
     NSString *type;
     
-    if (self.JSON && [[self.JSON allKeys] count] == 0) {
-        self.JSON = [[NSMutableDictionary alloc] initWithDictionary:[self reverseMapping]];
-    }
+    
     
     NSDictionary *properties = [PNObject propertiesForClass:self.class];
     
@@ -348,6 +346,10 @@ NSString * const PNObjectMappingSelector = @"selector";
         }
     }
     
+    if (self.JSON && [[self.JSON allKeys] count] == 0) {
+        self.JSON = JSON;
+    }
+    
     return JSON;
 }