Remove empty xray route paths, show 'No value' if no feature value available

frontend/src/metabase/routes.jsx

@@ -258,14 +258,8 @@ export const getRoutes = (store) =>
                     <Route path="table/:tableId/:cost" component={TableXRay} />
                     <Route path="field/:fieldId/:cost" component={FieldXRay} />
                     <Route path="card/:cardId/:cost" component={CardXRay} />
-                    <Route path="compare" title="Compare">
-                        <Route path="segments/:segmentId1/:segmentId2">
-                            <Route path=":cost" component={SegmentComparison} />
-                        </Route>
-                        <Route path="segment/:segmentId/table/:tableId">
-                            <Route path=":cost" component={SegmentTableComparison} />
-                        </Route>
-                    </Route>
+                    <Route path="compare/segments/:segmentId1/:segmentId2/:cost" component={SegmentComparison} />
+                    <Route path="compare/segment/:segmentId/table/:tableId/:cost" component={SegmentTableComparison} />
                 </Route>
 
                 {/* PULSE */}

frontend/src/metabase/xray/SimpleStat.jsx

@@ -14,7 +14,7 @@ const SimpleStat = ({ stat, showDescription }) =>
         </div>
         { /* call toString to ensure that values like true / false show up */ }
         <h1 className="my1">
-            {stat.value.toString()}
+            {stat.value ? stat.value.toString() : "No value"}
         </h1>
     </div>