title: how to avoid the error "Category member XXX defined as an empty set" in icCube?
body: <p>I've got the following MDX code to create a category dimension with 4 members:</p>
  
  <ul>
  <li>all members that make up of 0-50% of the measure (TopPercent)</li>
  <li>members 50-80%</li>
  <li>members 80-95%</li>
  <li>members 95-100%</li>
  </ul>
  
  <p>The code works perfectly on levels with a lot of members:</p>
  
  <pre><code>WITH
  MEMBER [measures].[v] as eval([Tijd].[Tijd].[jaar].[2018],[Measures].[Bedrag])
  
  set [selection] as Order( nonempty([Categorie].[Categorie].[categorie].members,[measures].[v]), [measures].[v], BDESC)  
  
  CATEGORY HIERARCHY [Stats].[ABCD], DEFAULT_MEMBER_NAME = "Totaal", LEVEL_NAME_PATTERN="L - ABCD - ${levelDepth}"
  CATEGORY MEMBER [Stats].[ABCD].[Totaal].[A (0-50%)] as
       TopPercent([selection],50, [measures].[v] ), ADD_CHILDREN=true
  CATEGORY MEMBER [Stats].[ABCD].[Totaal].[B (50-80%)] as
      TopPercent([selection],80, [measures].[v] )
      - TopPercent([selection],50, [measures].[v]), ADD_CHILDREN=true
  CATEGORY MEMBER [Stats].[ABCD].[Totaal].[C (80-95%)] as
      TopPercent([selection],95, [measures].[v])
      - TopPercent([selection],80, [measures].[v] ), ADD_CHILDREN=true
  CATEGORY MEMBER [Stats].[ABCD].[Totaal].[D (95-100%)] as
      Order([selection], [measures].[v], BDESC)
      - TopPercent([selection],95, [measures].[v]), ADD_CHILDREN=true
  
  SELECT
  // Measures
  {[measures].[v]} On 0,
  // Columns    
  [Stats].[ABCD].[L - ABCD - 1].members on 1,
  // Rows   
  [Stats].[ABCD].[L - ABCD - 2].members on 2
  FROM (select  [Tijd].[jaar].[2018] on 0 from [Spendzoom])
  /*ic3navigation*/
  </code></pre>
  
  <p>But when I run the MDX code with:</p>
  
  <pre><code>set [selection] as Order( nonempty([Categorie].[Categorie].[type].members,[measures].[v]), [measures].[v], BDESC)  
  </code></pre>
  
  <p>I get the error: <strong>Category member "[Stats].[ABCD].[Totaal].[C (80-95%)]'defined as an empty set.</strong></p>
  
  <p>I have tried to rewrite the definitions, as:</p>
  
  <pre><code>subcubeminus(TopPercent .... , TopPercent)
  </code></pre>
  
  <p>But that gave completely strange results.</p>
  
  <p>How can I overcome this error and have a generic approach that allways works regardless of the contents of the hierarchy &amp; level in the [selection] definition?</p>