new_contents: from imagekit.cachefiles import ImageCacheFile
  from nose.tools import assert_false
  from .imagegenerators import TestSpec
  
  
  def test_no_source():
      """
      Ensure sourceless specs are falsy.
      """
      spec = TestSpec(source=None)
      file = ImageCacheFile(spec)
      assert_false(bool(file))
  
subject: Add test to ensure sourceless specs are falsy