Adapt xsl to skip base classes which are not found

(and therefore have no name)

Author: Hauke Wintjen

Customization/xsl/class.xsl

@@ -84,18 +84,22 @@
           <b class="+ topic/ph hi-d/b "><xsl:value-of select="replace(compoundname,'^.*::','')"/></b>
           <xsl:choose>
             <xsl:when test="basecompoundref/@refid">
-              <xsl:variable name="extends" select="basecompoundref/@refid"/>
               <xsl:text> extends </xsl:text>
 
               <xsl:for-each select="basecompoundref">
+                <xsl:variable name="extends" select="@refid"/>
+                <xsl:variable name="extends-name" select="//compounddef[@id=$extends]/compoundname"/>
+                <xsl:if test="$extends-name">
+                  
                 <xsl:call-template name="add-link">
                   <xsl:with-param name="type" select="'topic'"/>
                   <xsl:with-param
                     name="href"
-                    select="concat('#',   dita-ot:name-to-id(//compounddef[@id=$extends]/compoundname))"
+                      select="concat('#',   dita-ot:name-to-id($extends-name))"
                   />
                   <xsl:with-param name="text" select="replace(.,'^.*\.','')"/>
                 </xsl:call-template>
+                </xsl:if>
                 <xsl:if test="count(basecompoundref) &gt; 1">
                   <xsl:text> </xsl:text>
                 </xsl:if>