old_contents: export default [
    {
      message:  'should remove a single null',
      fixture:  'a{margin:null}',
      expected: 'a{}'
    },
    {
      message:  'should break out right and left if top is null and right is defined',
      fixture:  'a{margin:null 1px}',
      expected: 'a{margin-right: 1px;margin-left: 1px}'
    },
    {
      message:  'should break out top and bottom if right is null and top is defined',
      fixture:  'a{margin:1px null}',
      expected: 'a{margin-top: 1px;margin-bottom: 1px}'
    },
    {
      message:  'should handle top and right defined with a null bottom',
      fixture:  'a{margin:1px 2px null}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-left: 2px}'
    },
    {
      message:  'should handle add defined with null top',
      fixture:  'a{margin:null 2px 3px 4px}',
      expected: 'a{margin-right: 2px;margin-bottom: 3px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null right',
      fixture:  'a{margin:1px null 3px 4px}',
      expected: 'a{margin-top: 1px;margin-bottom: 3px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null bottom',
      fixture:  'a{margin:1px 2px null 4px}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null left',
      fixture:  'a{margin:1px 2px 3px null}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-bottom: 3px}'
    },
    {
      message:  'should handle add defined with null right, left',
      fixture:  'a{margin:1px null 3px null}',
      expected: 'a{margin-top: 1px;margin-bottom: 3px}'
    },
    {
      message:  'should handle add defined with null top, bottom',
      fixture:  'a{margin:null 2px null 4px}',
      expected: 'a{margin-right: 2px;margin-left: 4px}'
    }
  ];
  
new_contents: export default [
    {
      message:  'should remove a single null',
      fixture:  'a{margin:null}',
      expected: 'a{}'
    },
    {
      message:  'should remove two nulls',
      fixture:  'a{margin:null null}',
      expected: 'a{}'
    },
    {
      message:  'should remove three nulls',
      fixture:  'a{margin:null null null}',
      expected: 'a{}'
    },
    {
      message:  'should remove four nulls',
      fixture:  'a{margin:null null null null}',
      expected: 'a{}'
    },
    {
      message:  'should break out right and left if top is null and right is defined',
      fixture:  'a{margin:null 1px}',
      expected: 'a{margin-right: 1px;margin-left: 1px}'
    },
    {
      message:  'should break out top and bottom if right is null and top is defined',
      fixture:  'a{margin:1px null}',
      expected: 'a{margin-top: 1px;margin-bottom: 1px}'
    },
    {
      message:  'should handle top and right defined with a null bottom',
      fixture:  'a{margin:1px 2px null}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-left: 2px}'
    },
    {
      message:  'should handle add defined with null top',
      fixture:  'a{margin:null 2px 3px 4px}',
      expected: 'a{margin-right: 2px;margin-bottom: 3px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null right',
      fixture:  'a{margin:1px null 3px 4px}',
      expected: 'a{margin-top: 1px;margin-bottom: 3px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null bottom',
      fixture:  'a{margin:1px 2px null 4px}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-left: 4px}'
    },
    {
      message:  'should handle add defined with null left',
      fixture:  'a{margin:1px 2px 3px null}',
      expected: 'a{margin-top: 1px;margin-right: 2px;margin-bottom: 3px}'
    },
    {
      message:  'should handle add defined with null right, left',
      fixture:  'a{margin:1px null 3px null}',
      expected: 'a{margin-top: 1px;margin-bottom: 3px}'
    },
    {
      message:  'should handle add defined with null top, bottom',
      fixture:  'a{margin:null 2px null 4px}',
      expected: 'a{margin-right: 2px;margin-left: 4px}'
    }
  ];
  
subject: Add more trbl tests