ui: add null check to txn details api

The txn details api was missing a null check when reading the
results of contention information, which lead to the showing of
an error when we should just not show any contention details.

Epic: none

Release note: None

pkg/ui/workspaces/cluster-ui/src/api/txnInsightsApi.ts

@@ -647,7 +647,7 @@ export async function getTxnInsightDetailsApi(
     if (!req.excludeContention && highContention) {
       const contentionInfo = await getTxnInsightsContentionDetailsApi(req);
       txnInsightDetails.blockingContentionDetails =
-        contentionInfo.blockingContentionDetails;
+        contentionInfo?.blockingContentionDetails;
     }
   } catch (e) {
     errors.contentionErr = e;