ENH: added display for empty values

src/core/css/webcaosdb.css

@@ -266,6 +266,14 @@ h5 {
     border-radius: 8px;
 }
 
+.caosdb-empty-value {
+    font-weight: bold;
+    font-size: 90%;
+    border: 1px solid #bbb;
+    padding: 2px 8px;
+    border-radius: 8px;
+}
+
 .caosdb-entity-panel-heading {
     border-bottom-left-radius: 3px;
     border-bottom-right-radius: 3px;  

src/core/xsl/entity.xsl

@@ -313,7 +313,7 @@
         <!-- DEPRECATED css class .caosdb-property-text-value - Use
              .caosdb-f-property-single-raw-value or introduce new 
              .caosdb-v-property-text-value -->
-        <span class="caosdb-f-property-single-raw-value caosdb-property-text-value"/>
+                <span class="caosdb-f-property-single-raw-value caosdb-property-text-value caosdb-empty-value">EMPTY</span>
       </xsl:otherwise>
     </xsl:choose>
   </xsl:template>