Don't make null track data rows in slice panel

Author: ALevansSamsung

ui/src/frontend/chrome_slice_panel.ts

@@ -522,6 +522,9 @@ export class ChromeSliceDetailsPanel extends SlicePanel {
               contents));
         const value = row.contents.value;
         if (typeof value === 'string') {
+          if (value === 'null') {
+            continue;
+          }
           renderedRow.push(m('td.value', this.mayLinkify(value)));
         } else {
           // Type of value being a record is not propagated into the callback