fix: DH-22392: Correctly test for absent axis calendar (#7939)

Author: niloc132

web/client-api/src/main/java/io/deephaven/web/client/api/widget/plot/JsAxis.java

@@ -35,10 +35,8 @@ public JsAxis(FigureDescriptor.AxisDescriptor descriptor, JsFigure jsFigure) {
         this.axis = descriptor;
         this.jsFigure = jsFigure;
 
-        final FigureDescriptor.BusinessCalendarDescriptor businessCalendarDescriptor =
-                descriptor.getBusinessCalendarDescriptor();
-        if (businessCalendarDescriptor != null) {
-            businessCalendar = new JsBusinessCalendar(businessCalendarDescriptor);
+        if (descriptor.hasBusinessCalendarDescriptor()) {
+            businessCalendar = new JsBusinessCalendar(descriptor.getBusinessCalendarDescriptor());
         } else {
             businessCalendar = null;
         }