title: strange warnings for transformable attribute
body: <p>I was using transformable attributes and everything work fine instead of those warnings:</p>
  
  <pre><code>15.10.11 22:14:07,191 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'directions' on entity 'DatabaseConnections'
  15.10.11 22:14:07,191 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'updateChoices' on entity 'DatabaseConnections'
  15.10.11 22:14:07,193 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'testingResult' on entity 'DestinationsListWeBuy'
  </code></pre>
  
  <p>may anybody tell how to move out this warning.
  for sure, everything is correct, attribute is optional, transformable.
  bellow is a class implementation:</p>
  
  <pre><code>#import &lt;Foundation/Foundation.h&gt;
  
  @interface ArrayToDataTransformer : NSValueTransformer {
  
  }
  
  @end
  
  
  
  #import "ArrayToDataTransformer.h"
  
  
  @implementation ArrayToDataTransformer
  
  + (BOOL)allowsReverseTransformation {
      return YES;
  }
  
  + (Class)transformedValueClass {
      return [NSData class];
  }
  
  - (id)transformedValue:(id)value {
      //Take an NSArray archive to NSData
      NSData *data = [NSKeyedArchiver archivedDataWithRootObject:value];
      return data;
  }
  
  - (id)reverseTransformedValue:(id)value {
      //Take NSData unarchive to NSArray 
      NSArray *array = (NSArray*)[NSKeyedUnarchiver unarchiveObjectWithData:value];
      return array;
  }
  
  @end
  </code></pre>