title: Subreport with return value gives exception "System is not facet valid with enumeration"
body: <p>I'm getting an exception during compile in Jaspersoft Studio 6.4.0.
  How do I address this?</p>
  
  <p>I've created a report containing a subreport from which I want to return a value. To do that, I have:</p>
  
  <ol>
  <li>Created a variable in the subreport called, "logTotal", set to the
  value of another variable, which is a summation calculated in the
  report. No reset type, no calculation function.</li>
  <li>Created a variable in the main report with the same name and type.
  No reset type, no calculation function.</li>
  <li>In the main report, created a subreport return value link
  between the two variables with calculation type, "System."</li>
  </ol>
  
  <p>On compile, I'm seeing the following exception:</p>
  
  <pre><code>net.sf.jasperreports.engine.JRException: org.xml.sax.SAXParseException; lineNumber: 454; columnNumber: 91; cvc-enumeration-valid: 
  Value 'System' is not facet-valid with respect to enumeration '[Nothing, Count, DistinctCount, Sum, Average, Lowest, Highest, StandardDeviation, Variance, First]'. It must be a value from the enumeration.
  </code></pre>
  
  <p>I can choose the "System" choice from a 
  If I use other choices ("No calculation function," "First," "Average," etc.), 
  the subreport returns null.</p>
  
  <p>Main Report:</p>
  
  <pre><code>&lt;variable name="logTotal" class="java.math.BigDecimal" resetType="None"/&gt;
  ...
  &lt;subreport&gt;
      &lt;reportElement positionType="Float" x="0" y="60" width="572" height="40" uuid="d3ec84fb-528f-41f5-8b54-26112fd95b50"/&gt;
      &lt;subreportParameter name="loadList"&gt;
          &lt;subreportParameterExpression&gt;&lt;![CDATA[$P{loadList}]]&gt;&lt;/subreportParameterExpression&gt;
      &lt;/subreportParameter&gt;
      &lt;connectionExpression&gt;&lt;![CDATA[$P{REPORT_CONNECTION}]]&gt;&lt;/connectionExpression&gt;
      &lt;returnValue subreportVariable="logTotal" toVariable="logTotal" calculation="System"/&gt;
      &lt;subreportExpression&gt;&lt;![CDATA["scaling/reports/ScaleSummary_Logs.jasper"]]&gt;&lt;/subreportExpression&gt;
  &lt;/subreport&gt;
  </code></pre>
  
  <p>Subreport:</p>
  
  <pre><code>&lt;variable name="price4" class="java.math.BigDecimal" calculation="Sum"&gt;
      &lt;variableExpression&gt;&lt;![CDATA[$F{price}]]&gt;&lt;/variableExpression&gt;
  &lt;/variable&gt;
  &lt;variable name="logTotal" class="java.math.BigDecimal" resetType="None"&gt;
      &lt;variableExpression&gt;&lt;![CDATA[$V{price4}]]&gt;&lt;/variableExpression&gt;
  &lt;/variable&gt;
  </code></pre>